MISTiC Winds is an approach to improve short-term weather forecasting based on a miniature high resolution, wide field, thermal emission spectrometry instrument that will provide global tropospheric vertical profiles of atmospheric temperature and humidity at high (3-4 km) horizontal and vertical ( 1 km) spatial resolution. MISTiC’s extraordinarily small size, payload mass of less than 15 kg, and minimal cooling requirements can be accommodated aboard a 27U-class CubeSat or an ESPA-Class micro-satellite. Low fabrication and launch costs enable a LEO sunsynchronous sounding constellation that would collectively provide frequent IR vertical profiles and vertically resolved atmospheric motion vector wind observations in the troposphere. These observations are highly complementary to present and emerging environmental observing systems, and would provide a combination of high vertical and horizontal resolution not provided by any other environmental observing system currently in operation. The spectral measurements that would be provided by MISTiC Winds are similar to those of NASA’s AIRS that was built by BAE Systems and operates aboard the AQUA satellite. These new observations, when assimilated into high resolution numerical weather models, would revolutionize short-term and severe weather forecasting, save lives, and support key economic decisions in the energy, air transport, and agriculture arenas–at much lower cost than providing these observations from geostationary orbit. In addition, this observation capability would be a critical tool for the study of transport processes for water vapor, clouds, pollution, and aerosols. Key remaining technical risks are being reduced through laboratory and airborne testing under NASA’s Instrument Incubator Program.
MISTiCTM Winds is an approach to improve short-term weather forecasting based on a miniature high resolution, wide field, thermal emission spectrometry instrument that will provide global tropospheric vertical profiles of atmospheric temperature and humidity at high (3-4 km) horizontal and vertical ( 1 km) spatial resolution. MISTiC’s extraordinarily small size, payload mass of less than 15 kg, and minimal cooling requirements can be accommodated aboard a 27U-class CubeSat or an ESPA-Class micro-satellite. Low fabrication and launch costs enable a LEO sunsynchronous sounding constellation that would collectively provide frequent IR vertical profiles and vertically resolved atmospheric motion vector wind observations in the troposphere. These observations are highly complementary to present and emerging environmental observing systems, and would provide a combination of high vertical and horizontal resolution not provided by any other environmental observing system currently in operation. The spectral measurements that would be provided by MISTiC Winds are similar to those of NASA’s AIRS that was built by BAE Systems and operates aboard the AQUA satellite. These new observations, when assimilated into high resolution numerical weather models, would revolutionize short-term and severe weather forecasting, save lives, and support key economic decisions in the energy, air transport, and agriculture arenas–at much lower cost than providing these observations from geostationary orbit. In addition, this observation capability would be a critical tool for the study of transport processes for water vapor, clouds, pollution, and aerosols. Key remaining technical risks are being reduced through laboratory and airborne testing under NASA’s Instrument Incubator Program.
A main objective of AIRS/AMSU on EOS is to provide accurate sounding products that are used to generate climate data sets. Suomi NPP carries CrIS/ATMS that were designed as follow-ons to AIRS/AMSU. Our objective is to generate a long term climate data set of products derived from CrIS/ATMS to serve as a continuation of the AIRS/AMSU products. We have modified an improved version of the operational AIRS Version-6 retrieval algorithm for use with CrIS/ATMS. CrIS/ATMS products are of very good quality, and are comparable to, and consistent with, those of AIRS.
This research uses General Circulation Model (GCM) derived products, with 1 km spatial resolution and sampled every 10 minutes, over a moving area following the track of a simulated severe Atlantic storm. Model products were aggregated over sounder footprints corresponding to 13 km in LEO, 2 km in LEO, and 5 km in GEO sampled every 72 minutes. We simulated radiances for instruments with AIRS-like spectral coverage, spectral resolution, and channel noise, using these aggregated products as the truth, and analyzed them using a slightly modified version of the operational AIRS Version-6 retrieval algorithm. Accuracy of retrievals obtained using simulated AIRS radiances with a 13 km footprint was similar to that obtained using real AIRS data. Spatial coverage and accuracy of retrievals are shown for all three sounding scenarios. The research demonstrates the potential significance of flying Advanced AIRS-like instruments on future LEO and GEO missions.
The atmospheric infrared sounder (AIRS) science team version-6 AIRS/advanced microwave sounding unit (AMSU) retrieval algorithm is now operational at the Goddard Data and Information Services Center (DISC). AIRS version-6 level-2 products are generated near real time at the Goddard DISC and all level-2 and level-3 products are available starting from September 2002. Some of the significant improvements in retrieval methodology contained in the version-6 retrieval algorithm compared to that previously used in version-5 are described. In particular, the AIRS science team made major improvements with regard to the algorithms used to (1) derive surface skin temperature and surface spectral emissivity; (2) generate the initial state used to start the cloud clearing and retrieval procedures; and (3) derive error estimates and use them for quality control. Significant improvements have also been made in the generation of cloud parameters. In addition to the basic AIRS/AMSU mode, version-6 also operates in an AIRS only (AO) mode, which produces results almost as good as those of the full AIRS/AMSU mode. The improvements of some AIRS version-6 and version-6 AO products compared to those obtained using version-5 are also demonstrated.
The high cost of imaging and sounding from space warrants exploration of new methods for obtaining the required information, including changing the spectral band sets, employing new technologies and merging instruments. In some cases we must consider relaxation of the current capability. In others, we expect higher performance. In general our goal is to meet the VIIRS and CrIS requirements while providing the enhanced next generation capabilities: 1) Hyperspectral Imaging in the Vis/NIR bands, 2) High Spatial Resolution Sounding in the Infrared bands. The former will improve the accuracy of ocean color products, aerosols and water vapor, surface vegetation and geology. The latter will enable the high-impact achieved by the current suite of hyperspectral infrared sounders to be achieved by the next generation high resolution forecast models. We examine the spectral, spatial and radiometric requirements for a next generation system and technologies that can be applied from the available inventory within government and industry. A two-band grating spectrometer instrument called the Moderate-resolution Infrared Imaging Sounder (MIRIS) is conceived that, when used with the planned NASA PACE Ocean Color Instrument (OCI) will meet the vast majority of CrIS and VIIRS requirements in the all bands and provide the next generation capabilities desired. MIRIS resource requirements are modest and the Technology Readiness Level is high leading to the expectation that the cost and risk of MIRIS will be reasonable.
AIRS was launched on EOS Aqua in May 2002, together with AMSU-A and HSB (which subsequently failed early in the mission), to form a next generation polar orbiting infrared and microwave atmospheric sounding system. AIRS/AMSU had two primary objectives. The first objective was to provide real-time data products available for use by the operational Numerical Weather Prediction Centers in a data assimilation mode to improve the skill of their subsequent forecasts. The second objective was to provide accurate unbiased sounding products with good spatial coverage that are used to generate stable multi-year climate data sets to study the earth’s interannual variability, climate processes, and possibly long-term trends. AIRS/AMSU data for all time periods are now being processed using the state of the art AIRS Science Team Version-6 retrieval methodology. The Suomi-NPP mission was launched in October 2011 as part of a sequence of Low Earth Orbiting satellite missions under the “Joint Polar Satellite System” (JPSS). NPP carries CrIS and ATMS, which are advanced infra-red and microwave atmospheric sounders that were designed as follow-ons to the AIRS and AMSU instruments. The main objective of this work is to assess whether CrIS/ATMS will be an adequate replacement for AIRS/AMSU from the perspective of the generation of accurate and consistent long term climate data records, or if improved instruments should be developed for future flight. It is critical for CrIS/ATMS to be processed using an algorithm similar to, or at least comparable to, AIRS Version-6 before such an assessment can be made. We have been conducting research to optimize products derived from CrIS/ATMS observations using a scientific approach analogous to the AIRS Version-6 retrieval algorithm. Our latest research uses Version-5.70 of the CrIS/ATMS retrieval algorithm, which is otherwise analogous to AIRS Version-6, but does not yet contain the benefit of use of a Neural-Net first guess start-up system which significantly improved results of AIRS Version-6. Version-5.70 CrIS/ATMS temperature profile and surface skin temperature retrievals are of very good quality, and are better than AIRS Version-5 retrievals, but are still significantly poorer than those of AIRS Version-6. CrIS/ATMS retrievals should improve when a Neural-Net start-up system is ready for use. We also examined CrIS/ATMS retrievals generated by NOAA using their NUCAPS retrieval algorithm, which is based on earlier versions of the AIRS Science Team retrieval algorithms. We show that the NUCAPS algorithm as currently configured is not well suited for climate monitoring purposes.
The NASA Goddard Earth Sciences (GES) Data and Information Services Center (DISC) generates products derived
from AIRS/AMSU-A observations, starting from September 2002 when the AIRS instrument became stable, using the
AIRS Science Team Version-5 retrieval algorithm. This paper shows results of some of our research using Version-5
products from the points of view of improving forecast skill as well as aiding in the understanding of climate processes.
The Goddard DISC generated products derived from AIRS/AMSU-A observations, starting from September 2002 when
the AIRS instrument became stable, using the AIRS Science Team Version-5 retrieval algorithm. The AIRS Science
Team Version-6 retrieval algorithm became operational at the Goddard DISC in late 2012. This paper describes some of
the significant improvements in retrieval methodology contained in the Version-6 retrieval algorithm, compared to that
used in Version-5. In particular, the Science Team made major changes with regard to the algorithms used to 1) derive
surface skin temperature and surface spectral emissivity; 2) generate the initial state used to start the cloud clearing and
retrieval procedures; and 3) determine Quality Control. This paper describes these advances found in the AIRS Version-
6 retrieval algorithm and demonstrates the improvements of some AIRS Version-6 products compared to those obtained
using Version-5.
This paper compares recent spatial anomaly time series of OLR (Outgoing Longwave Radiation) and OLRCLR (Clear Sky
OLR) as determined using CERES and AIRS observations over the time period September 2002 through June 2010. We
find excellent agreement in OLR anomaly time series of both data sets in almost every detail, down to the 1° x 1° spatial
grid point level. This extremely close agreement of OLR anomaly time series derived from observations by two different
instruments implies that both sets of results must be highly stable. This agreement also validates to some extent the
anomaly time series of the AIRS derived products used in the computation of the AIRS OLR product. The paper then
examines anomaly time series of AIRS derived products over the extended time period September 2002 through April
2011. We show that OLR anomalies during this period are closely in phase with those of an El Niño index, and that
recent global and tropical mean decreases in OLR and OLRCLR are a result of a transition from an El Niño condition at
the beginning of the data record to La Niña conditions toward the end of the data period. This relationship can be
explained by temporal changes of the distribution of mid-tropospheric water vapor and cloud cover in two spatial regions
that are in direct response to El Niño/La Niña activity which occurs outside these spatial regions.
The Goddard DISC has generated products derived from AIRS/AMSU-A observations, starting from September 2002 when the AIRS instrument became stable, using the AIRS Science Team Version-5 retrieval algorithm. The AIRS Science Team Version-6 retrieval algorithm will be finalized in September 2011. This paper describes some of the significant improvements contained in the Version-6 retrieval algorithm, compared to that used in Version-5, with an emphasis on the improvement of atmospheric temperature profiles, ocean and land surface skin temperatures, and ocean and land surface spectral emissivities. AIRS contains 2378 spectral channels covering portions of the spectral region 650 cm-1 (15.38 μm) - 2665 cm-1 (3.752 μm). These spectral regions contain significant absorption features from two CO2 absorption bands, the 15 μm (longwave) CO2 band, and the 4.3 μm (shortwave) CO2 absorption band. There are also two atmospheric window regions, the 12 μm - 8 μm (longwave) window, and the 4.17 μm - 3.75 μm (shortwave) window. Historically, determination of surface and atmospheric temperatures from satellite observations was performed using primarily observations in the longwave window and CO2 absorption regions. According to cloud clearing theory, more accurate soundings of both surface skin and atmospheric temperatures can be obtained under partial cloud cover conditions if one uses observations in longwave channels to determine coefficients which generate cloud cleared radiances Ri for all channels, and uses Ri only from shortwave channels in the determination of surface and atmospheric temperatures. This procedure is now being used in the AIRS Version-6 Retrieval Algorithm. Results are presented for both daytime and nighttime conditions showing improved Version-6 surface and atmospheric soundings under partial cloud cover.
KEYWORDS: Clouds, Error analysis, Temperature metrology, Climatology, Data modeling, Algorithms, Data processing, Space operations, Data centers, Physics
The AIRS Science Team Version 5 retrieval algorithm has been finalized and is now operational at the Goddard DAAC
in the processing (and reprocessing) of all AIRS data. The AIRS Science Team Version 5 retrieval algorithm contains
two significant improvements over Version 4: 1) Improved physics allows for use of AIRS observations in the entire
4.3 μm CO2 absorption band in the retrieval of temperature profile T(p) during both day and night. Tropospheric
sounding 15 μm CO2 observations are now used primarily in the generation of cloud cleared radiances Ri. This approach
allows for the generation of accurate values of Ri and T(p) under most cloud conditions. 2) Another very significant
improvement in Version 5 is the ability to generate accurate case-by-case, level-by-level error estimates for the
atmospheric temperature profile, as well as for channel-by-channel error estimates for Ri. These error estimates are used
for Quality Control of the retrieved products.
We have conducted forecast impact experiments assimilating AIRS temperature profiles with different levels of Quality
Control using the NASA GEOS-5 data assimilation system. Assimilation of Quality Controlled T(p) resulted in
significantly improved forecast skill compared to that obtained from analyses obtained when all data used operationally
by NCEP, except for AIRS data, is assimilated. We also conducted an experiment assimilating AIRS radiances
uncontaminated by clouds, as done operationally by ECMWF and NCEP. Forecast resulting from assimilated AIRS
radiances were of poorer quality than those obtained assimilating AIRS temperatures.
AIRS was launched on EOS Aqua on May 4, 2002, together with AMSU-A and HSB, to form a next generation polar
orbiting infrared and microwave atmospheric sounding system. AIRS is a grating spectrometer with a number of linear
arrays of detectors with each detector sensitive to outgoing radiation in a characteristic frequency υi with a spectral band
pass Δυi of roughly υi/1200 AIRS contains 2378 spectral channels covering portions of the spectral region 650 cm-1
(15.38 μm) - 2665 cm-1 (3.752 μm). These spectral regions contain significant absorption features from two CO2
absorption bands, the 15 μm (longwave) CO2 band, and the 4.3 μm (shortwave) CO2 absorption band. There are also two
atmospheric window regions, the 12 μm - 8 μm (longwave) window, and the 4.17 μm - 3.75 μm (shortwave) window.
Historically, determination of surface and atmospheric temperatures from satellite observations was performed using
primarily observations in the longwave window and CO2 absorption regions. One reason for this was concerns about the
effects, during the day, of reflected sunlight and non-Local Thermodynamic Equilibrium (non-LTE) on the observed
radiances in the shortwave portion of the spectrum. According to cloud clearing theory, more accurate soundings of both
surface skin and atmospheric temperatures can be obtained under partial cloud cover conditions if one uses the longwave
channels to determine cloud cleared radiances Ri for all channels, and uses Ri only from shortwave channels in the
determination of surface and atmospheric temperatures. This procedure is now being used by the AIRS Science Team in
preparation for the AIRS Version 6 Retrieval Algorithm. This paper describes how the effects on the radiances of solar
radiation reflected by clouds and the Earth's surface, and also of non-LTE, are accounted for in the analysis of the data.
Results are presented for both daytime and nighttime conditions showing improved surface and atmospheric soundings
under partial cloud cover resulted from not using Ri in the retrieval process for any longwave channels sensitive to cloud
effects. This improvement is made possible because AIRS NEDT in the shortwave portion of the spectrum is extremely
low.
Hyperspectral infrared atmospheric sounders (e.g. the Atmospheric Infrared Sounder (AIRS) on Aqua and the Infrared
Atmospheric Sounding Interferometer (IASI) on MetOp) provide highly accurate temperature and water vapor profiles
in the lower to upper troposphere. These systems are vital operational components of our National Weather Prediction
system and the AIRS has demonstrated over 6 hrs of forecast improvement on the 5 day operational forecast1. Despite
the success in the mid troposphere to lower stratosphere, a reduction in sensitivity and accuracy has been seen in these systems in the boundary layer over land. In this paper we demonstrate the potential improvement associated with higher spatial resolution (1km vs currently 13.5 km) on the accuracy of boundary layer products with an added consequence of higher yield of cloud free scenes. This latter feature is related to the number of samples that can be assimilated and has also shown to have a significant impact on improving forecast accuracy. We also present a set of frequencies and resolutions that will improve vertical resolution of temperature and water vapor and trace gas species throughout the atmosphere. Development of an Advanced Low Earth Orbit (LEO) Sounder (ALS) with these improvements will improve weather forecast at the regional scale and of tropical storms and hurricanes. Improvements are also expected in the accuracy of the water vapor and cloud properties products, enhancing process studies and providing a better match to the resolution of future climate models. The improvements of technology required for the ALS are consistent with the current state of technology as demonstrated in NASA Instrument Incubator Program and NOAA's Hyperspectral Environmental Suite (HES) formulation phase development programs.
The AIRS Science Team Version 5.0 retrieval algorithm became operational at the Goddard DAAC in July 2007
generating near real-time products from analysis of AIRS/AMSU sounding data. This algorithm contains many
significant theoretical advances over the AIRS Science Team Version 4.0 retrieval algorithm used previously. Two very
significant developments of Version 5 are: 1) the development and implementation of an improved Radiative Transfer
Algorithm (RTA) which allows for accurate treatment of non-Local Thermodynamic Equilibrium (non-LTE) effects on
shortwave sounding channels; and 2) the development of methodology to obtain very accurate case by case product error
estimates which are in turn used for quality control. These theoretical improvements taken together enabled a new
methodology to be developed which further improves soundings in partially cloudy conditions. In this methodology,
longwave CO2 channel observations in the spectral region 700 cm-1 to 750 cm-1 are used exclusively for cloud clearing
purposes, while shortwave CO2 channels in the spectral region 2195 cm-1 to 2395 cm-1 are used for temperature sounding
purposes. This allows for accurate temperature soundings under more difficult cloud conditions. This paper further
improves on the methodology used in Version 5 to derive surface skin temperature and surface spectral emissivity from
AIRS/AMSU observations. Now, following the approach used to improve tropospheric temperature profiles, surface
skin temperature is also derived using only shortwave window channels. This produces improved surface parameters,
both day and night, compared to what was obtained in Version 5. These in turn result in improved boundary layer
temperatures and retrieved total O3 burden.
The AIRS instrument is currently the best space-based tool to simultaneously monitor the vertical distribution of
key climatically important atmospheric parameters as well as surface properties, and has provided high
quality data for more than 5 years. AIRS analysis results produced at the GODDARD/DAAC, based on
Versions 4 & 5 of the AIRS retrieval algorithm, are currently available for public use. Here, first we present
an assessment of interrelationships of anomalies (proxies of climate variability based on 5 full years, since Sept.
2002) of various climate parameters at different spatial scales. We also present AIRS-retrievals-based global,
regional and 1x1 degree grid-scale "trend"-analyses of important atmospheric parameters for this 5-year period.
Note that here "trend" simply means the linear fit to the anomaly (relative the mean seasonal cycle) time series
of various parameters at the above-mentioned spatial scales, and we present these to illustrate the usefulness of
continuing AIRS-based climate observations. Preliminary validation efforts, in terms of intercomparisons of
interannual variabilities with other available satellite data analysis results, will also be addressed. For example,
we show that the outgoing longwave radiation (OLR) interannual spatial variabilities from the available state-of-the-art CERES measurements and from the AIRS computations are in remarkably good agreement. Version
6 of the AIRS retrieval scheme (currently under development) promises to further improve bias agreements for
the absolute values by implementing a more accurate radiative transfer model for the OLR computations and by
improving surface emissivity retrievals.
The AIRS Science Team Version 5.0 retrieval algorithm became operational at the Goddard DAAC in July 2007
generating near real-time products from analysis of AIRS/AMSU sounding data. This algorithm contains many
significant theoretical advances over the AIRS Science Team Version 4.0 retrieval algorithm used previously. Three
very significant developments of Version 5 are: 1) the development and implementation of an improved Radiative
Transfer Algorithm (RTA) which allows for accurate treatment of non-Local Thermodynamic Equilibrium (non-LTE)
effects on shortwave sounding channels; 2) the development of methodology to obtain very accurate case by case
product error estimates which are in turn used for quality control; and 3) development of an accurate AIRS only cloud
clearing and retrieval system. These theoretical improvements taken together enabled a new methodology to be
developed which further improves soundings in partially cloudy conditions, without the need for microwave
observations in the cloud clearing step as has been done previously. In this methodology, longwave CO2 channel
observations in the spectral region 700 cm-1 to 750 cm-1 are used exclusively for cloud clearing purposes, while
shortwave CO2 channels in the spectral region 2195 cm-1 to 2395 cm-1 are used for temperature sounding purposes. The
new methodology for improved error estimates and their use in quality control is described briefly and results are shown
indicative of their accuracy. Results are also shown of forecast impact experiments assimilating AIRS Version 5.0
retrieval products in the Goddard GEOS 5 Data Assimilation System using different quality control thresholds.
Satellites provide an ideal platform to study the Earth-atmosphere system on practically all spatial and temporal
scales. Thus, one may expect that their rapidly growing datasets could provide crucial insights not only for
short-term weather processes/predictions but into ongoing and future climate change processes as well. Though
Earth-observing satellites have been around for decades, extracting climatically reliable information from their
widely varying datasets faces rather formidable challenges. AIRS/AMSU is a state of the art
infrared/microwave sounding system that was launched on the EOS Aqua platform on May 4, 2002, and has
been providing operational quality measurements since September 2002. In addition to temperature and
atmospheric constituent profiles, outgoing longwave radiation [OLR] and basic cloud parameters are also
derived from the AIRS/AMSU observations. However, so far the AIRS products have not been rigorously
evaluated/validated on a large scale. Here we present preliminary assessments of climatically important
"Level3" (monthly and 8-day means, 1° x 1° gridded) AIRS "Version 4.0" retrieved products (available to the
public through the DAAC at NASA/GSFC) to assess their utility for climate studies. Though the current AIRS
climatology covers only ~4.5 years, it will hopefully extend much further into the future. First we present
"consistency checks" by evaluating the ~4.5-yr long time series of global and tropical means, as well as grid-scale
variability and "anomalies" (relative to the first full years worth of AIRS "climate statistics" of several
climatically important retrieved parameters). Finally, we also present preliminary results regarding
interrelationships of some of these geophysical variables, to assess to what extent they are consistent with the
known physics of climate variability/change. In particular, we find at least one observed relationship which
contradicts current general circulation climate (GCM) model results: the global water vapor climate feedback
which is expected to be strongly positive is deduced to be slightly negative (shades of the "Lindzen effect"?).
The AIRS Science Team Version 5.0 retrieval algorithm will become operational at the Goddard DAAC in early 2007 in the near real-time analysis of AIRS/AMSU sounding data. This algorithm contains many significant theoretical advances over the AIRS Science Team Version 4.0 retrieval algorithm used previously. Three very significant developments are:
1) the development and implementation of a very accurate Radiative Transfer Algorithm (RTA) which allows for accurate treatment of non-Local Thermodynamic Equilibrium (non-LTE) effects on shortwave sounding channels; 2) the development of methodology to obtain very accurate case by case product error estimates which are in turn used for quality control; and 3) development of an accurate AIRS only cloud clearing and retrieval system. These theoretical improvements taken together enabled a new methodology to be developed which further improves soundings in partially cloudy conditions, without the need for microwave observations in the cloud clearing step as has been done previously. In this methodology, longwave CO2 channel observations in the spectral region 700 cm-1 to 750 cm-1 are used exclusively for cloud clearing purposes, while shortwave CO2 channels in the spectral region 2195 cm-1 to 2395 cm-1 are used for temperature sounding purposes. The new methodology is described briefly and results are shown, including comparison with those using AIRS Version 4, as well as a forecast impact experiment assimilating AIRS Version 5.0 retrieval products in the Goddard GEOS 5 Data Assimilation System.
The AIRS instrument was launched in May 2002 into a polar sun-synchronous orbit onboard the EOS Aqua Spacecraft. Since then we have released three versions of the AIRS data product to the scientific community. AIRS, in conjunction with the Advanced Microwave Sounding Unit (AMSU), produces temperature profiles with 1K/km accuracy on a global scale, as well as water vapor profiles and trace gas amounts. The first version of software, Version 2.0 was available to scientists shortly after launch with Version 3.0 released to the public in June 2003. Like all AIRS product releases, all products are accessible to the public in order to have the best user feedback on issues that appear in the data. Fortunately the products have had exceptional accuracy and stability. This paper presents the improvement between AIRS Version 4.0 and Version 5.0 products and shows examples of the new products available in Version 5.0.
The Atmospheric Infrared Sounder (AIRS) sounding suite, launched in 2002, is the most advanced atmospheric
sounding system to date, with measurement accuracies far surpassing those of current operational weather satellites.
From its sun-synchronous polar orbit, the AIRS system provides more than 300,000 all-weather soundings covering
more than 90% of the globe every 24 hours. Usage of AIRS data products, available to all through the archive system
operated by NASA, is spreading throughout the atmospheric and climate research community. An ongoing validation
effort has confirmed that the system is very accurate and stable and is close to meeting the goal of providing global
temperature soundings with an accuracy of 1 K per 1-km layer and water vapor soundings with an accuracy of 20%
throughout the troposphere, surpassing the accuracy of radiosondes. This unprecedented data set is currently used for
operational weather prediction in a number of countries, yielding significant positive impact on forecast accuracy and
range. It is also enabling more detailed investigations of current issues in atmospheric and climate research. In addition
to the basic soundings related to the hydrologic cycle, AIRS also measures a number of trace gases, the latest such
product being the global distribution of carbon dioxide. We discuss some examples of recent research with AIRS data.
AIRS was launched on EOS Aqua on May 4, 2002, together with AMSU-A and HSB, to form a next generation polar orbiting infrared and microwave atmospheric sounding system. The primary products of AIRS/AMSU-A are twice daily global fields of atmospheric temperature-humidity profiles, ozone profiles, sea/land surface skin temperature, and cloud related parameters including OLR. The sounding goals of AIRS are to produce 1 km tropospheric layer mean temperatures with an rms error of 1K, and layer precipitable water with an rms error of 20 percent, in cases with up to 80 percent effective cloud cover. The basic theory used to analyze AIRS/AMSU/HSB data in the presence of clouds, called the at-launch algorithm, and a post-launch algorithm which differed only in the minor details from the at-launch algorithm, have been described previously. The post-launch algorithm, referred to as AIRS Version 4, has been used by the Goddard DAAC to analyze and distribute AIRS retrieval products. In this paper we show two candidates for the AIRS Version 5 algorithm which will be used by the Goddard DAAC starting late in 2006. The methodology used in each is otherwise identical, but one version uses only AIRS observations in the generation of cloud cleared radiances, while the other uses both AIRS and AMSU-A observations as done previously. Improvements made to the retrieval algorithm since Version 4 are described as well as results comparing retrieval accuracy and spatial coverage of each candidate for Version 5 with each other and with those obtained using Version 4.
Global energy balance of the Earth-atmosphere system may change due to natural and man-made climate
variations. For example, changes in the outgoing longwave radiation (OLR) can be regarded as a crucial
indicator of climate variations. Clouds play an important role -still insufficiently assessed- in the global energy
balance on all spatial and temporal scales, and satellites provide an ideal platform to measure cloud and largescale
atmospheric variables simultaneously. The TOVS series of satellites were the first to provide this type of
information since 1979. OLR [Mehta and Susskind1], cloud cover and cloud top pressure [Susskind et al.2] are
among the key climatic parameters computed by the TOVS Pathfinder Path-A algorithm using mainly the
retrieved temperature and moisture profiles. AIRS, regarded as the 'new and improved TOVS', has a much
higher spectral resolution and greater S/N ratio, retrieving climatic parameters with higher accuracy.
First we present encouraging agreements between MODIS and AIRS cloud top pressure (Ctp) and
'effective' (Aeff, a product of infrared emissivity at 11 μm and physical cloud cover or Ac) cloud fraction
seasonal and interannual variabilities for selected months. Next we present validation efforts and preliminary
trend analyses of TOVS-retrieved Ctp and Aeff. For example, decadal global trends of the TOVS Path-A and
ISCCP-D2 Pc and Aeff/Ac values are similar. Furthermore, the TOVS Path-A and ISCCP-AVHRR [available
since 1983] cloud fractions correlate even more strongly, including regional trends.
We also present TOVS and AIRS OLR validation effort results and (for the longer-term TOVS Pathfinder
Path-A dataset) trend analyses. OLR interannual spatial variabilities from the available state-of-the-art CERES
measurements and both from the AIRS [Susskind et al.3,4] and TOVS OLR computations are in remarkably
good agreement. Global monthly mean CERES and TOVS OLR time series show very good agreement in
absolute values also. Finally, we will assess correlations among long-term trends of selected parameters,
derived simultaneously from the TOVS Pathfinder Path-A dataset.
AIRS contains 2376 high spectral resolution channels between 650 cm-1 and 2665 cm-1, including channels in both the
15 micron (near 667 cm-1) and 4.2 micron (near 2400 cm-1) CO2 sounding bands. Use of temperature sounding channels
in the 15 micron CO2 band has considerable heritage in infra-red remote sensing. Channels in the 4.2 micron CO2 band
have potential advantages for temperature sounding purposes because they are essentially insensitive to absorption by
water vapor and ozone, and also have considerably sharper lower tropospheric temperature sounding weighting
functions than do the 15 micron temperature sounding channels. Potential drawbacks with regard to use of 4.2 micron
channels arise from effects on the observed radiances of solar radiation reflected by the surface and clouds, as well as
effects of non-local thermodynamic equilibrium on shortwave observations during the day. These are of no practical
consequences, however, when properly accounted for. We show results of experiments performed utilizing different
spectral regions of AIRS, conducted with the AIRS Science Team candidate Version 5 algorithm. Experiments were
performed using temperature sounding channels within the entire AIRS spectral coverage, within only the spectral region
650 cm-1 to 1614 cm-1; and within only the spectral region 1000 cm-1-2665 cm-1. These show the relative importance of
utilizing only 15 micron temperature sounding clouds, only the 4.2 micron temperature sounding channels, and both,
with regards to sounding accuracy. The spectral region 2380 cm-1 to 2400 cm-1 is shown to contribute significantly to
improve sounding accuracy in the lower troposphere, both day and night.
AIRS was launched on EOS Aqua on May 4, 2002, together with AMSU A and HSB, to form a next generation polar
orbiting infrared and microwave atmospheric sounding system. The primary products of AIRS/AMSU are twice daily
global fields of atmospheric temperature-humidity profiles, ozone profiles, sea/land surface skin temperature, and cloud
related parameters including OLR. The sounding goals of AIRS are to produce 1 km tropospheric layer mean
temperatures with an rms error of 1K, and layer precipitable water with an rms error of 20 percent, in cases with up to 80
percent effective cloud cover. The basic theory used to analyze AIRS/AMSU/HSB data in the presence of clouds, called
the at-launch algorithm, and a post-launch algorithm which differed only in the minor details from the at-launch
algorithm, have been described previously. The post-launch algorithm, referred to as AIRS Version 4.0, has been used
by the Goddard DAAC to analyze and distribute AIRS retrieval products. In this paper we show progress made toward
the AIRS Version 5.0 algorithm which will be used by the Goddard DAAC starting late in 2006. A new methodology
has been developed to provide accurate case by case error estimates for retrieved geophysical parameters and for the
channel by channel cloud cleared radiances used to derive the geophysical parameters from the AIRS/AMSU
observations. These error estimates are in turn used for quality control of the derived geophysical parameters and clear
column radiances. Improvements made to the retrieval algorithm since Version 4.0 are described as well as results
comparing Version 5.0 retrieval accuracy and spatial coverage with those obtained using Version 4.0.
The Earth Science and Meteorological communities are taking great interest in a new instrument released by NASA. The Atmospheric Infrared Sounder (AIRS), launched on the EOS Aqua Spacecraft on May 4, 2002, is a high spectral resolution infrared imaging spectrometer with over 2300 distinct infrared wavelengths ranging from 3.7 μm to 15.4 μm. AIRS is unique in that it provides the highest infrared spectral resolution to date while also providing coverage of over 95% of the Earth's surface every day at 15 km spatial resolution. The AIRS project is currently managed by NASA's Jet Propulsion Laboratory in Pasadena, California1. The AIRS is providing a wealth of scientific data to the Earth Science community including upper atmospheric water vapor and atmospheric composition on key greenhouse gases. It is also improving weather forecasting and the studies of processes affecting climate and weather.
Simultaneous use of AIRS/AMSU-A observations allow for the determination of accurate atmospheric soundings under partial cloud cover conditions. The methodology involves the determination of the radiances AIRS would have seen if the AIRS fields of view were clear, called clear column radiances, and use of these radiances to infer the atmospheric and surface conditions giving rise to these clear column radiances. Susskind et al. demonstrate via simulation that accurate temperature soundings and clear column radiances can be derived from AIRS/AMSU-A observations in cases of up to 80% partial cloud cover, with only a small degradation in accuracy compared to that obtained in clear scenes. Susskind and Atlas show that these findings hold for real AIRS/AMSU-A soundings as well. For data assimilation purposes, this small degradation in accuracy is more than offset by a significant increase in spatial coverage (roughly 50% of global cases were accepted, compared to 3.6% of the global cases being diagnosed as clear), and assimilation of AIRS temperature soundings in partially cloudy conditions resulted in a larger improvement in forecast skill than when AIRS soundings were assimilated only under clear conditions. Alternatively, derived AIRS clear column radiances under partial cloud cover could also be used for data assimilation purposes. Further improvements in AIRS sounding methodology have been made since the results shown in Susskind and Atlas. A new version of the AIRS/AMSU-A retrieval algorithm, Version 4.0, was delivered to the Goddard DAAC in February 2005 for production of AIRS derived products, including clear column radiances. The major improvement in the Version 4.0 retrieval algorithm is with regard to a more flexible, parameter dependent, quality control. Results are shown of the accuracy and spatial distribution of temperature-moisture profiles and clear column radiances derived from AIRS/AMSU-A as a function of fractional cloud cover using the Version 4.0 algorithm. Use of the Version 4.0 AIRS temperature profiles increased the positive forecast impact arising from AIRS retrievals relative to what was shown in Susskind and Atlas.
The AIRS/AMSU (flying on the EOS-AQUA satellite) sounding retrieval methodology allows for the retrieval of key atmospheric/surface parameters under partially cloudy conditions (Susskind et al., 2003). In addition, cloud parameters are also derived from the AIRS/AMSU observations. Within each AIRS footprint, cloud parameters at up to 2 cloud layers are determined with differing cloud top pressures and "effective" (product of infrared emissivity at 11 microns and physical cloud fraction) cloud fractions. However, so far the AIRS cloud product has not been rigorously evaluated/validated. Fortunately, collocated/coincident radiances measured by MODIS/AQUA (at a much lower spectral resolution but roughly an order of-magnitude higher spatial resolution than that of AIRS) are used to determine analogous cloud products from MODIS. This allows us for a rather rare and interesting possibility: the intercomparisons and mutual validation of imager vs. sounder-based cloud products obtained from the same satellite positions. First, we present results of small-scale (granules) instantaneous intercomparisons. Next, we will evaluate differences of temporally averaged (monthly) means as well as the representation of inter-annual variability of cloud parameters as presented by the two cloud data sets. In particular, we present statistical differences in the retrieved parameters of cloud fraction and cloud top pressure. We will investigate what type of cloud systems are retrieved most consistently (if any) with both retrieval schemes, and attempt to assess reasons behind statistically significant differences.
AIRS was launched on EOS Aqua on May 4, 2002, together with AMSU A and HSB, to form a next generation polar orbiting infrared and microwave atmospheric sounding system. The primary products of AIRS/AMSU/HSB are twice daily global fields of atmospheric temperature-humidity profiles, ozone profiles, sea/land surface skin temperature, and cloud related parameters including OLR. The sounding goals of AIRS are to produce 1 km tropospheric layer mean temperatures with an rms error of 1K, and 1 km tropospheric layer precipitable water with an rms error of 20%, in cases with up to 80% effective cloud cover. Pre-launch simulation studies indicated that these results should be achievable. Minor modifications have been made to the pre-launch retrieval algorithm as alluded to in this paper. Sample fields of parameters retrieved from AIRS/AMSU/HSB data are presented and temperature profiles are validated as a function of retrieved effective fractional cloud cover. As in simulation, the degradation of retrieval accuracy with increasing cloud cover is small. Select fields are also compared to those contained in the ECMWF analysis, done without the benefit of AIRS data, to demonstrate information that AIRS can add to that already contained in the ECMWF analysis with regard to daily, monthly mean, and interannual differences of monthly mean fields.
The National Oceanic and Atmospheric Administration (NOAA) is considering a microwave radiometer for the next series of Geostationary Operational Environmental Satellites (GOES-R) to be launched starting in 2012. This paper examines the products proposed for the geostationary microwave radiometer in the light of current microwave retrieval algorithms and estimates the performance achievable from geostationary altitude with a three-meter antenna. The results suggest that hemispheric soundings and rain rates can be generated on an hourly basis with the desired accuracy and horizontal resolution, that capping inversions can be detected in conjunction with infrared soundings, that hurricane warm core temperatures can be resolved using high frequencies plus deconvolution and that ocean wind and total precipitable water products can be provided with close to the desired resolution.
There are several microwave instruments in low Earth orbit (LEO) that are used for atmospheric temperature and humidity sounding by themselves and in conjunction with companion IR sounders. These instruments have achieved a certain degree of maturity and are undergoing a redesign to minimize their size, mass, and power requirements from the previous generation instruments. An example of these instruments is the AMSU-A series, now flying on POES and Aqua spacecraft, with the IR sounders HIRS3 and AIRS respectively. These older microwave instruments are going to be replaced by the ATMS instruments that will fly on NPP and NPOESS satellites with the CrIS IR sounder. A number of enabling technologies acquired from the ATMS instrument hardware design and data processing are directly applicable to performing similar microwave sounding on a geostationary platform. Because these technologies are already in place, they are readily available for the development of a geostationary orbit (GEO) microwave instrument, thereby avoiding costly technology development and minimizing the risk of not achieving the scientific requirements. In fact, the MMIC microwave components that were developed by ATMS for size and volume reduction are directly applicable to a GEO microwave sounder.
The benefits of microwave sounders are well known. They penetrate non-precipitating cloud cover and allow for accurate soundings obtained with a collocated high spectral resolution IR sounder in up to 80% cloud cover. The key advantages of a microwave instrument in GEO will be its ability to provide high temporal resolution and uniform spatial resolution, and it will expand the utility of a collocated advanced IR sounder to cases in which partial cloud cover exists. A footprint in the order of 100 km by 100 km resolution with hemispherical coverage within one hour can be easily achieved for sounding channels in the 50 to 57 GHz range. A GEO microwave sounder will also allow mesoscale sampling of select regions.
AIRS was launched on EOS Aqua on May 4, 2002, together with AMSU A and HSB, to form a next generation polar orbiting infrared and microwave atmospheric sounding system. The primary products of AIRS/AMSU/HSB are twice daily global fields of atmospheric temperature-humidity profiles, ozone profiles, sea/land surface skin temperature, and cloud related parameters including OLR. The sounding goals of AIRS are to produce 1 km tropospheric layer mean temperatures with an rms error of 1K, and 1 km tropospheric layer precipitable water with an rms error of 20%, in cases with up to 80% effective cloud cover. Pre-launch simulation studies indicated that these results should be achievable. Minor modifications have been made to the pre-launch retrieval algorithm as alluded to in this paper. Sample fields of parameters retrieved from AIRS/AMSU/HSB data are presented and temperature profiles are validated as a function of retrieved effective fractional cloud cover. As in simulation, the degradation of retrieval accuracy with increasing cloud cover is small. Select fields are also compared to those contained in the ECMWF analysis, done without the benefit of AIRS data, to demonstrate information that AIRS can add to that already contained in the ECMWF analysis. Assimilation of AIRS temperature soundings in up to 80% cloud cover for the month of January 2003 into the GSFC FVSSI data assimilation system resulted in improved 5 day forecasts globally, both with regard to anomaly correlation coefficients and the prediction of location and intensity of cyclones.
AIRS was launched on EOS Aqua on May 5 2002, together with AMSU A and HSB, to form a next generation polar orbiting infrared and microwave atmospheric sounding system. The primary products of AIRS/AMSU/HSB are twice daily global fields of atmospheric temperature-humidity profiles, ozone profiles, sea/land surface skin temperature, and cloud related parameters including OLR. The sounding goals of AIRS are to produce 1 km tropospheric layer mean temperatures with an rms error of 1K, and layer precipitable water with an rms error of 20%, in cases with up to 80% effective cloud cover. Pre-launch simulation studies indicated that these results should be achievable. Minor modifications have been made to the pre-launch retrieval algorithm as described in this paper. Sample fields of parameters retrieved from AIRS/AMSU/HSB data are presented and validated as a function of retrieved fractional cloud cover. As in simulation, the degradation of retrieval accuracy with increasing cloud cover is small. Select fields are also compared to those contained in the ECMWF analysis, done without the benefit of AIRS data, to demonstrate information that AIRS can add to that already contained in the ECMWF analysis.
In previous studies, desert-fringe vegetation densities were assessed in an ungrazed semi-arid rangeland in Utah and in an animal exclosure in the arid Sinai. Applying satellite measurements of reflectances, the dark vertical cylinders (DVC) model for desert-scrub (characterized by predominantly vertical architecture) was inverted. In the present study a new plane-parallel model is presented, which treats the canopy as a layer of small Lambertian spheres (SLS), or small facets (leaves) with a specific distribution of the leaf area, where the Schonberg function of the angle between the solar beam and the view direction specifies the reflectance from the canopy. The SLS model is inverted with the satellite-measured reflectances of the Sinai exclosure and the surrounding overgrazed, practically bare-soil terrain. The SLS-model inversion results are compared with DVC results. Both models provide plausible canopy characterizations, but the SLS model is more realistic when viewing from the zenith with sun at a high elevation. The reflectance ratio of the dark plant-elements to the bright soil is key to assessing the density of the plants. In the inversion of the AVHRR visible and near-infrared data, the plant element reflectances in the infrared are adjusted so that the plant optical density in the infrared matches that determined in the visible spectral region. Early in the dry summer season (after the winter rains), high infrared reflectances are inferred, but sharply lower infrared reflectances, appropriate for the dried out plants, are found in the later stages of the dry season. This result, that the physical changes in the plant conditions can be assessed, is highly encouraging for our SLS modeling effort.
The NOAA polar low earth orbit operational satellites carry HIRS2/MSU instruments and thus have thermal and microwave remote sensing capability. The measurements have been processed for retrieval of surface and atmospheric meteorological parameters using a version of the Goddard Laboratory for Atmospheres (GLA) interactive forecast-retrieval-analysis system. This interactive approach has properties that make it desirable for derivation of climate data sets, because it provides for accurate treatment of the effects of clouds on the IR radiances and elimination of some systematic errors form the retrieved quantities. The use of the microwave MSU cloud-penetrating wavelengths adds significantly to the remote sensing capabilities for the retrievals, as it allows for use of thermal data under partial cloud cover as high as 80%. Interannual differences of atmospheric temperatures derived from HIRS2/MSU on NOAA 10 show good quantitive agreement with values obtained from radiosonde reports. As part of the TOVS Pathfinder program, the retrieval system will be frozen to produce a 15 year (1979 - 1994) set of satellite-derived surface and atmospheric parameters. Data for the years 1986, 1987, and 1988 based on the current retrieval analysis are now available.
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