The US operates a diverse, evolving constellation of research and operational environmental satellites, principally in polar and geosynchronous orbits. Our current and enhanced future domestic remote sensing capability is complemented by the significant capabilities of our current and potential future international partners. In this analysis, we define "success" through the data customers' "eyes": participating in the sufficient and continuously improving satisfaction of their mission responsibilities. To successfully fuse together observations from multiple simultaneous platforms and sensors into a common, self-consistent, operational environment requires that there exist a unified calibration and validation approach. Here, we consider develop a concept for an integrating framework for absolute accuracy; long-term stability; self-consistency among sensors, platforms, techniques, and observing systems; and validation and characterization of performance. Across all systems, this is a non-trivial problem. Simultaneous Nadir Overpasses, or SNO's, provide a proven intercomparison technique: simultaneous, collocated, co-angular measurements. Many systems have off-nadir elements, or effects, that must be calibrated. For these systems, the nadir technique constrains the process. We define the term "SOON," for simultaneous overpass off nadir. We present a target architecture and sensitivity analysis for the affordable, sustainable implementation of a global SOON calibration/validation network that can deliver the much-needed comprehensive, common, self-consistent operational picture in near-real time, at an affordable cost.

Numerical weather prediction and climate change detection studies critically depend on accurate, reliable, and consistent satellite radiance data from multiple sensors onboard a constellation of satellites. The calibration consistency across international satellites is further challenged in the implementation of GEOSS (Global Earth Observation System of Systems). As a result, establishing on-orbit calibration links among operational satellite radiometers has become critical. This paper provides an overview of the current status and challenges in the on-orbit calibration traceability among operational satellite radiometers. It then proposes to develop an on-orbit calibration reference network to establish the calibration links. The Simultaneous Nadir Overpass method for intersatellite calibration is a key methodology for the network. Other methodologies including vicarious calibration, moon calibration, and airborne campaigns will also be used to support the network. Example applications of the network for operational satellite radiometers are demonstrated. By establishing an on-orbit calibration network that makes the calibration of similar radiometers traceable to each other, a quasi on-orbit calibration standard can be established in the long-term. The system will help us diagnose radiance biases for data assimilation and time series analysis. It will also bring together a world of radiometers to facilitate the implementation of GEOSS.

The state-of-the-art electro-optical sensors being designed for today's space-based environmental applications require a complete characterization and thorough calibration. This is especially true for sensors designed to assess global climate change, which require very small uncertainties. This paper describes a system-level approach that addresses each phase of calibration, from planning to on-orbit operations. This approach encourages early planning and continuity of effort throughout the lifetime of the project (pre- and post-flight) to promote an optimum calibration approach that will minimize uncertainty for the intended application. This paper also discusses considerations for component level characterization, ground calibration and standards, in-flight calibration sources and trending, and in-flight validation assessment.

We review the advantages of a national standard for microwave brightness temperature and outline our proposed approach toward developing such a standard. The proposal is a combined standard that would comprise both a standard radiometer, traceable to primary noise standards, and a fully characterized standard target. We also review our recent work on development of a standard radiometer and on characterization of calibration targets.

Exploiting the redundancy in high spectral resolution observations, dependent set Principle Component Analysis (PCA) is a simple yet very powerful tool not only for noise filtering and lossy compression, but also for the characterization of sensor noise and other variable artifacts using Earth scene data. Our approach for dependent set PCA of AIRS Earth scene data is presented. Aspects of the analyses include 1) estimation of NEDT using PCA and comparisons to values derived from on-board blackbodies, 2) estimation of the scene dependence of NEDN, 3) estimation of the spectrally correlated component of NEDT and comparison to pre-launch analyses using blackbody views, 4) investigation of non- Gaussian noise behavior, and 5) inspection of individual PCs. The results of the PCA analyses are generally consistent with results obtained pre-launch and on-orbit using blackbody and/or space view data. Specific findings include: 1) PCA estimates of AIRS spectrally random and spectrally correlated NEDN compare well with estimates computed from on-board blackbody and space views, 2) the signal dependence of AIRS NEDN is accurately parameterized in terms of the scene radiance, 3) examination of the reconstruction error allows non-Gaussian phenomenon such as popping to be characterized, and 4) inspection of the PCs and individual PC filtered radiance spectra is a powerful technique for diagnosing low level artifacts in hyperspectral data.

Atmospheric soundings derived from Global Positioning System radio occultations (GPSRO) acquired in low-Earth orbit have the potential to be global climate benchmark observations of significant value to the Global Climate Observing System (GCOS). Geophysical observables such as atmospheric pressure and temperature are derived by measuring propagation delay induced by the atmosphere, a measurement whose fundamental unit-the second-is absolutely determined by calibration against atomic clocks. In this paper, we analyze the sources of systematic and random error for GPSRO soundings to determine the steps needed to establish GPSRO as a climate benchmark observation. Benchmarks require specific processing strategies and specific forms of documentation so that confidence in the accuracy and precision of the measurements is assured. Establishing calibration traceability to absolute standards (SI-traceability) is an essential strategy. We discuss a wide range of error sources in a geophysical retrieval, such as orbit determination error, signal delay in the Earth's ionosphere, and quality control strategies. Uncalibrated ionospheric delay is identified as the error source deserving the most attention in establishing SI-traceability of the retrievals, to meet stringent climate observation requirements of 0.5 K accuracy and 0.04 K stability. Profile comparisons from the recently launched COSMIC constellation establish strong upper limits on systematic error arising from the individual instruments. These encouraging results suggest that GPSRO should become a permanent resource for the GCOS. These highly precise and accurate instruments can be deployed on future Earth Observation satellites at a low per-sensor cost and minimal interference to existing and planned observational programs.

A data collection experiment was held on 10 May 2006 in which various types of ground truth were collected. During analysis of the data, it became apparent that a good deal of temporal and spatial variability existed both between the two collection sites and between each of the flight lines. The variability was primarily manifested in the total sky radiance spectra collected during each flight line. These effects were believed to be due to a rapidly changing sky environment populated by sparse clouds that grew thicker as the collection continued. After discussing the theoretical considerations of remotely sensing in the presence of clouds and other objects, the results of our analysis are presented. It was observed that temporal variability resulted in approximately 2-15% error in sky radiance across the visible wavelengths, and that spatial variability in sky radiance could be shown to be responsible for up to 5% error in retrieved reflectance. Additional theoretical work in modeling the expected radiance contributions of a cloudy sky and the impacts of cloud-induced variability is on-going and will be supported by these results.

The Atmospheric Infrared Sounder (AIRS) and MODerate-Resolution Imaging Spectroradiometer (MODIS) on board the EOS Aqua spacecraft measure the upwelling infrared radiance used for numerous remote sensing and climate related applications. AIRS provides high spectral resolution infrared radiances while MODIS provides collocated high spatial resolution radiances at sixteen broad infrared bands. An optimal algorithm for cloud-clearing has been developed for AIRS cloudy soundings at the University of Wisconsin-Madison where the spatially and spectrally collocated AIRS and MODIS data has been used to verify this algorithm. A global analysis and characterization of the AIRS cloud-clearing using the bias and the standard deviation between AIRS cloud-cleared brightness temperature and the nearby clear brightness temperature are studied.

A detailed evaluation of the latest version of WINDSAT surface wind data has recently been performed to determine the quality of these data and their usefulness for ocean surface wind analysis and numerical weather prediction. The first component of this evaluation consisted of both subjective and objective comparisons of WINDSAT wind vectors to other sources of ocean surface winds (eg. ship and buoy observations, Quikscat satellite winds, or model derived wind analyses). This was followed by data impact experiments using a variational surface wind analysis, as well as an operational four-dimensional data assimilation system. The results of this evaluation demonstrate the usefulness of WINDSAT data, but also show deficiencies relative to current scatterometer measurements.

Validation is an important but particularly challenging task for passive microwave remote sensing of soil moisture from Earth orbit. The key issue is spatial scale; conventional measurements of soil moisture are made at a point whereas satellite sensors provide an integrated area/volume value for a much larger spatial extent. For microwave remote sensing from space it is necessary to consider the kilometer to 40 km scale, which presents new challenges. This issue of spatial scale is common to both current and future satellite missions. Regardless of the degree of difficulty, ground based sampling must remain a core component of validation. An integrated approach using in situ networks, field campaigns and comparison to other satellite products is described.

The CrIS and ATMS instruments on NPOESS will provide high quality temperature and moisture profiles greatly surpassing the capabilities of current operational satellite sounders. However, performance of these systems continues to be a challenge in cloudy scenes. The VIIRS sensor on NPOESS will provide much higher spatial resolution data than that of CrIS, with some overlap in spectral coverage. This sub-pixel information can be used to enhance the retrieval performance in a number of ways. This paper presents a potential technique to improve performance of the CrIS temperature profile retrievals by incorporating data from VIIRS. Improvements include more accurate retrievals in partly cloudy situations, better effective spatial resolution and more robust quality control diagnostics. We provide an overview of our approach and show examples utilizing data from the EOS-Aqua AIRS, AMSU and MODIS sensors.

Future instruments will improve atmospheric measurements in both time and space. Although these data are expected to advance traditional Numerical Weather Prediction (NWP) guidance at 48 hours and beyond, greater benefit may come from objective nowcasting systems that assist forecasters in identifying rapidly developing and isolated extreme weather events a few hours in advance. These systems should detect and retain extreme variations in the atmosphere and incorporate large volumes of high-resolution asynoptic data. Because they need to be extremely fast, they may use numerical approaches different from current NWP. A new objective nowcasting approach is presented that uses trajectories to optimize the impact and retention of satellite information. It is designed to detect and preserve intense vertical and horizontal variations observed over time. Real data tests have identified atmospheric details associated with the onset of significant weather events up to 6 hours in advance. Using full resolution moisture products from current GOES sounders to update and enhance current operational forecasts, the Lagrangian system captures and retains details (maxima, minima and extreme gradients) important to the development of convective instability, even after IR observations are no longer available due to cloud development. Examples of the issues and impact of using hyperspectral AIRS data are also discussed.

In order to meet the requirements, documented by the Geostationary Operational Environmental Satellite (GOES) user communities, the instruments designated for the GOES-R notional baseline include an Advanced Baseline Imager (ABI), a Hyperspectral Environmental Suite (HES), a Geostationary Lightning Mapper (GLM), and advanced space and solar observing instruments including the Solar Imaging Suite (SIS) and the Space Environment In-Situ Suite (SEISS). These instruments will monitor a wide range of phenomena, including applications relating to: weather, climate, ocean, coastal zones, land, hazards, solar and space.

Large thunderstorms can be identified in the AIRS data as areas where the brightness temperature of the 1231 cm-1 atmospheric window channel in non-polar areas is less than 210 K. Each day about 6000 large thunderstorms are identified by this test, almost exclusively within 30 degrees of the equator. Since the size of the AIRS footprint at nadir is 13.5 km, a brightness temperature of less than 210 K indicates that the top of the anvil of the thunderstorm protrudes well into the tropopause. Such objects are commonly referred to as Deep Convective Clouds (DCC). Our interest in DCC was motivated by the question "Are severe weather events increasing due to global warming". Each DCC is a severe weather event, although not on the scale of the much less frequent hurricanes, which can be identified in the AIRS data as clusters of several hundred DCC. For the past four years the number of DCC per day has been fairly stable for all tropical oceans combined, but a significant increase can be seen day and night in the Atlantic Ocean. This increase may be related to the slowing of the Atlantic meridional overturning circulation. The most prominent features in brightness temperature spectra of DCC are due to stratospheric CO2, Ozone and Methane. In the channels with weighting functions below the stratosphere the brightness temperature is typically 205 K, with a characteristic 1 to 2.5 K drop between 1000 and 750 cm-1, equivalent to a 2-4 % drop in emissivity. This is likely due to the presence of cirrus (ice) particles. Firmer conclusions about the significance of the DCC count require a considerably longer data set than the currently available four years from AIRS. We plan to continue this analysis with AIRS data. Extension of the analysis to past operational sounders in polar orbit requires independent validation of the stability and absolute accuracy of the radiometric calibration at 210 K. AIRS is an imaging hyperspectral grating-array spectrometer on the EOS Aqua spacecraft, launched on May 4, 2002.

Based on TBB data from GMS of Japan, NCEP/NCAR reanalysis data and precipitation data from CPC Merged Analysis of Precipitation (CMAP), an investigation is carried out of seasonal changes of precipitation and convection over Asian-Australian "land bridge" areas and its possible factors. The results show that the precipitation and convection over Sumatra take on clearly seasonal changes with abundant (less) rainfall in winter (summer). The convection over Sumatra moves northwestward rapidly along "land bridge" in the late-April and the early-May (the 25th pentad) and the rainfall shows similar variations. It is the rapid northwestward shifting of convection that affects directly the subsequent enhancement of the convection over Indo-China Peninsula (ICP) area followed by the rupture of the subtropical high (SH) bands in this region leading to South China Sea (SCS) summer monsoon establishment. The zonal wind at lower troposphere in the equatorial Indian Ocean and the cross equatorial flow in 105°E are the main factors associated with the rapid northwestward shifting of convection along "land bridge".

A linear mathematical error model for the assessment of validation activity of atmospheric retrievals is presented. The purpose of the validation activity is to assess the actual performance of the remote sensing validated system while in orbit by comparing its measurements to some relevant-validating-data sets. The validating system samples volumes of the atmosphere at times and locations that are different from the ones when and where the validated system makes its own observations. The location of the validating system can be either stationary, e.g. a ground ARM site, or movable, e.g. an aircraft or some other satellites. The true states may be correlated or not. The sampled volumes differ from each other by their location, timing, and size. The validated and validating systems have different vertical resolution and grid, absolute accuracy, and noise level. All the above factors cause apparent differences between the data to be compared. The validation assessment model makes the comparison accurate by allowing for the differences. The model can be used for assessment and interpretation of the validation results when the above mentioned sources of discrepancies are significant, as well as for evaluation of a particular validating data source.

Based on NCEP/NCAR reanalysis data, an investigation has been carried of climatic features of East Asian subtropical summer monsoon trough (sub-trough) and its comparison to South China Sea summer monsoon trough (SCS trough). The results show that the SCS trough is stronger than the sub-trough, whether convergence or convection. The sub-trough extends to higher level and inclines northward with altitude, but the SCS trough is reversed. The SCS trough onsets early and abruptly with the positive relative vorticity appearing suddenly and retreats slowly, but the sub-trough establishes step by step with the positive relative vorticity over Yunnan and Guizhou tableland and Guangxi areas spreading northeastward and withdraws rapidly. It is an obvious indicator that the easterly reverses the westerly during the SCS trough's onset, but the sub-trough establishment is characteristic of the westerly enhancement. The sub-trough has clearly frontal property, but the SCS trough is opposite.

Through analyzing the mesoscale disturbance field of a Meiyu rainstorm, it is found that there are close relations between the development and propagation of inertia-gravitational waves, rain belts and low vortex. The propagating patterns of inertia-gravitational waves are different in the upper and lower levels. In the early period of precipitation, convective instability triggers the inertia-gravitational waves. When there are inertia-gravitational waves propagating southward in the upper and lower levels, it is favorable to form multi-rain belts. In the mid of precipitation, the inertia-gravitational waves in the upper-layer rotate anticlockwise with the lower-layer vortex center, and precipitation strengthens and moves eastward in the meantime. The inertia-gravitational waves propagating northward in the upperlayer may result in the development of the lower-layer vortex and precipitation.

EOF analysis has been conducted of the interdecadal variability of sea temperature anomaly fields at standard levels in the subsurface, and the abrupt change feature of sea temperature has been tested by use of movable t-test technique. A possible mechanism of the ocean-air system in the tropical Pacific is investigated by using the subsurface temperature, heat storage and wind stress data, leading to the main results as follows. The analysis indicates that around 1980 there occurs a significant interdecadal abrupt change of temperature from sea surface to different depths, of which 4 modes show the accident and their formation is closely related to the southwestward subduction route of North Pacific sea temperature anomalies. The interdecadal signal of subduction in the window region of the North Pacific propagates southwestward to the subtropics, meeting the anomalous signal which propagates northeastward from the western Pacific at ~ 160-meter level in the thermocline. Therefore, the influence of the former on ENSO interdecadal variability might be indirect while the latter plays a more important role. The western tropical South Pacific, which displays evident interdecadal variability, is the key region of the ENSO interdecadal variability. The positive temperature anomaly will move to the mid-tropical Pacific and the atmospheric response will excite an anticyclonic wind stress to the east of Australia, which will lead to the generation of a negative temperature anomaly in the tropical southwest Pacific. A similar evolution with an opposite sign will follow subsequently. The whole cycle takes about 13 years to complete.

In the context of daily rainfall from 58 stations in South China and day-to-day gridded reanalysis from NCEP/NCAR, study is performed of April-June precipitation features at different time intervals in the research area in relation to the establishment of summer monsoon in the South-China Sea (SCS). Results show that the rainfall consists of frontal and monsoon rainfall, the former occurring dominantly in April and the latter largely in June as its principal phase, indicating that the vapor transport, dynamic and thermal features vary greatly for both. Further analysis shows that the amount of the frontal precipitation bears an intimate relation to the time of monsoon onset. In the year of deficient frontal rainfall the Sri Lanka vortex appears earlier and spreads northwards, in combination with northward-advancing convective band from Sumatra to cause the Indo-Burma trough to be established, as well as the subtropical high-pressure belt to break and eastward retreat - all happen earlier than usual, a situation that favors the establishment of westerlies in the SCS, leading to earlier establishment of SCS summer monsoon. In years of plentiful frontal rainfall, however, the formation of the Bengal Bay trough depends mainly on the displacement of Sumatra convection into the Indo-China peninsula, a situation unfavorable for the earlier breaking of the subtropical high-pressure belt and its eastward movement, resulting in later establishment of west winds in the SCS, so that SCS summer monsoon has its establishment delayed.

As a major agrometeorological disaster of winter wheat in Henan, drought is a big contributing factor to the steady rise of the yield. To make risk assessment of the drought-caused yield decline is of much significance to rational choice of culvars and putting forth measures against drought loss. Based on interannual meteorological and yield records, analysis is undertaken of yearly drought probability, percentage yield decline and yield coefficient of variation, whereupon is constructed a model for comprehensive risk assessment of wheat yield and regionalized is the risk happening. Evidence suggests that the indices of the risk assessment range over 1.23 ~ 4.88, with the high-value zones making up 12.5%, distributed mainly in eastern, and northeastern Henan, the middle-value zones accounting for 36.5% in southwest, southeast, eastern, northeast and northwest Henan and the low-value zones (51.0%) in the extensive region, with Lushi - Xiangcheng (Beijing to Guangzhou railway in Henan) as the axis line in the east - west (south - north) Henan province.

Doppler radar, when used in detecting large-scale intense precipitation, has its echo features differing than those from warm or cold advection alone (as an S- or anti-S- form) and than those just from large-scale convergence or divergence (as a bow-like shape) but the features of Doppler velocity resulting from the combination of warm or cold advection with convergence or divergence are called the complex windfield. Analysis of Doppler weather radar data from an extensive, persistent strong rainfall event over the Hai river basin on August 16, 2005 reveals that 1) in the presence of a low-level complex windfield related to the combination of warm advection and convergence, i.e., the Doppler velocity products show that, starting from the radar center, clockwise curvature of a zero-speed line on one side toward the positive velocity zone is more remarkable than the counterpart on the other side towards the negative velocity zone, implying that when the negative speed zone is bigger compared to the maximum positive area, rainfall is reinforced or maintained; 2) in the presence of a low-level complex windfield resulting from warm advection combined with divergence, the precipitation would be weakened or ceased. Therefore, the study on the convergence and divergence in the radar velocity field gives a good indicator of nowcasting prediction of the formation, development, maintenance and decay phases of a large-scale rainfall event.

Using the sea surface temperature (SSTA) and wind anomalies (SSWA) of the tropical Pacific from January 1970 to December 1989,main spatial patterns of tropical Pacific SSTA and SSWA coupling features in the transform course from the warm phase to the cold phase of El Nino-southern oscillation (ENSO) cycles are discussed. The main conclusions are as follows: 1) air-sea coupling patterns at the mature stage of El Nino (La Nina) are main spatial ones of tropical Pacific SSWA and SSTA coupling; 2) at the mature stage of El Nino, the interaction of the anticgclonic anomaly wind,generated by the forcing of distinct meridional SSTA gradient in the northern Hemisphere tropical central Pacific, with the California cold current and SSTA is mainly responsible for weakening of El Nino; 3) the second sea temperature increase along the south American coast in the decaying course of El Nino results from the eastward movement of the weakened positive SSTA in the tropical central-eastern Pacific forced by anomalous west wind stress; 4) La Nina results from the joint effect of Walker circulation, Ekman drift and negative SSTA in the tropical central-eastern Pacific.

Future satellite weather instruments such as high spectral resolution imaging interferometers pose a challenge to the atmospheric science and software development communities due to the immense data volumes they will generate. An open-source, scalable reference software implementation demonstrating the calibration of radiance products from an imaging interferometer, the Geosynchronous Imaging Fourier Transform Spectrometer1 (GIFTS), is presented. This paper covers essential design principles laid out in summary system diagrams, lessons learned during implementation and preliminary test results from the GIFTS Information Processing System (GIPS) prototype.