Satellite observations of tropospheric carbon monoxide (CO) are employed in diverse applications including air quality studies, chemical weather forecasting and the characterization of CO emissions through inverse modeling. The TERRA / MOPITT ('Measurements of Pollution in the Troposphere') instrument incorporates a set of gas correlation radiometers to observe CO simultaneously in both a thermal-infrared (TIR) band near 4.7 µm and a near-infrared (NIR) band near 2.3 μm. This multispectral capability is unique to MOPITT. The MOPITT retrieval algorithm for vertical profiles of CO has been refined almost continuously since TERRA was launched at the end of 1999. Retrieval algorithm enhancements are the result of ongoing analyses of instrument performance, improved radiative transfer modeling, and systematic comparisons with correlative data, including in-situ profiles measured from aircraft and products from other satellite instruments. In the following, we describe the methods used to routinely evaluate MOPITT CO profiles. As the satellite instrument with the longest record for CO, methods for assessing the long-term stability are becoming increasingly important.
The High Resolution Dynamics Limb Sounder (HIRDLS) instrument is a 21-channel limb scanning infrared radiometer,
designed to make global measurements of temperature, ozone, water vapor, eight other gases and aerosols from 8 to as
high as 80 km. with 1 km. vertical resolution. During launch on NASA’S Aura satellite a piece of interior lining
material became lodged in the foreoptics, reducing the effective aperture by 80-95%, and inserting another signal into
the system. The HIRDLS team has worked for several years to develop corrections for these effects, and recover as
many as possible of the planned capabilities. This talk describes the last and probably final set of algorithms to recover
the planned species. Early work developed corrections for channels with large radiances allowing temperature and
ozone to be retrieved. Subsequent work has concentrated on refining these to allow species such as nitric acid,
chlorofluorocarbons 11 & 12, nitrogen dioxide, N2O5, chlorine nitrate, nitrous oxide and water vapor to be recovered.
Effort has gone into studying, then parameterizing in an adaptive way, the quasi-regular way the signal from the
blockage varies with time during an orbit and during the mission. Several recent improvements are described. Results of
these corrections show improvements in the retrieved products.
A piece of plastic film came loose during launch and blocked most of the optical aperture. The largest remaining
problem in correcting the measured radiances is the removal of the signals from this blockage. The present method is
briefly described, followed by an outline of a new version, called the (ST)3 method. It relies on more understanding of
the behavior of the blockage signals acquired in previous work. The method involves Scaling and Time interpolating the
signals, Shifting them to align features, and Translating them to recover the scaled value at the reference angle. The
residuals are represented by empirical orthogonal functions, coefficients of which may be Substituted from other
channels. Finally, allowance for long-term Temporal changes in the blockage signals are being developed. Results for a
day in the middle of the mission are presented, as well as their effects on water vapor retrievals.
The High Resolution Dynamics Limb Sounder (HIRDLS) instrument was launched on the NASA Aura satellite in July
2004. HIRDLS is a joint project between the UK and USA, and is a mid-infrared limb emission sounder designed to
measure the concentrations of trace species, cloud and aerosol, and temperature and pressure variations in the Earth's
atmosphere from the upper troposphere to the mesosphere. The instrument is intended to make measurements at both
high vertical and horizontal spatial resolutions, but validating those measurements is difficult because few other
measurements provide that vertical resolution sufficiently closely in time. However, the FORMOSAT-3/COSMIC suite
of radio occultation satellites that exploit the U.S. GPS transmitters to obtain high resolution (~1 km) temperature
profiles in the stratosphere does provide sufficient profiles nearly coincident with those from HIRDLS. Comparisons
show a good degree intercorrelation between COSMIC and HIRDLS down to about 2 km resolution, with similar
amplitudes for each, implying that HIRDLS and COSMIC are able to measure the same small scale features. The
optical blockage that occurred within HIRDLS during launch does not seem to have affected this capability.
The HIRDLS instrument is a limb viewing infra-red radiometer on the NASA Aura spacecraft in a sun synchronous low
earth orbit and obtains measurements of the composition of the atmosphere covering the whole Earth each day. The
MIPAS instrument is a limb viewing infra-red interferometer on board the European Envisat satellite in a very similar
orbit to Aura except that the local solar time is different. The complement of geophysical data products of both
instruments is very similar, and because of similar observation strategies their two data sets can be usefully compared.
The comparison provides the means to support validation in order to obtain statistics such as systematic differences and
variance. This is performed over the full latitude range of HIRDLS and height range of MIPAS and thereby helps to
identify sources of errors. The identification of known atmospheric features is a useful diagnostic, and includes such
things as regions of upwelling of tracer gases, or the propagation of coherent structures as with mid-latitude waves and
we can test whether these structures are consistently represented in both data sets. HIRDLS version 2.04.19 (v004)
temperature, ozone and nitric acid show very low systematic 'errors' compared to MIPAS over most of the spatial range.
Currently pre-released water vapour, nitrous oxide and F-11 are reasonably similar, CH4 somewhat more restricted, and
nitrogen dioxide, N2O5, chlorine nitrate and F-12 as yet susceptible to complications from the obstructed telescope.
Further details are discussed in the paper.
The data assimilation of 2000-2004 carbon monoxide (CO) retrievals by the MOPITT (Measurements Of Pollution In The Troposphere) instrument onboard the NASA Terra satellite provide an opportunity for the first time to study the transport and sources of pollution including their year-to-year variations. Based on the different representations of assimilated CO in the chemistry transport model (CTM) space and at the MOPITT retrieval grid this study advocates for direct mapping of CO-sensitive radiances or characterized CO retrievals by the chemical data assimilation schemes. The comprehensive CO forecast provides a great deal of information on the vertical scales that cannot be constrained by the measured radiances. It also provides comprehensive a priori specifications for the inverse problems especially for the vertical levels and geographical regions where the radiometer begins to misplace its high sensitivity to the CO loading. Evaluation of the multi-year MOPITT retrievals and assimilated CO against in situ CO statistics showed how the data assimilation helps to diminish a priori effects in the reprocessed CO retrievals. Data analysis of the multi-year data reveal substantial inter-annual variations of CO loading in the free troposphere and call for the unbiased tracer assimilation schemes in the CTM with optimized CO surface emissions.
The functional performance of the NASA Aura HIRDLS instrument since launch on the 15th July 2004 is presented and discussed. The HIRDLS (High Resolution Infra-red Limb Sounder) is a 21-channel infra-red radiometer, using actively cooled MCT detectors on a common focal plane. It has many features that provide considerable flexibility of the commanding, control and the format and content of the telemetry. HIRDLS also features a precision 2-axis scan mirror
and gyroscopes that are attached to the optical bench and together they provide additional data on the line of sight on small time scales. The stability of the temperature control of the focal plane and critical optical components is also presented and discussed. To-date the instrument has performed functionally without fault and in many aspects well within specifications. The only problem (and a serious one) so far encountered has been the optical blockage of the main aperture, which is discussed in other papers. Some aspects of the instrument that have been utilised to help characterise the blockage are outlined.
The High Resolution Dynamics Limb Sounder (HIRDLS) instrument was launched on NASA's Aura spacecraft on 15 July 2004. When activation was completed 25 days later, it was discovered that the measured radiances were very different from those that were expected. After a long series of analyses and diagnostic tests, the cause was confirmed to be a blockage that covers much of the front aperture, preventing even one completely clear view of the atmosphere. In this paper the steps required to correct the radiances for the effects of the blockage are noted. These are calibrating the radiances, removing the effects of the blockage oscillating, and the radiance coming from the blockage, correcting for the effects of the partial aperture, and filtering the noise. The paper describes the algorithms needed, and presents the results of their application. The success of the procedures will be demonstrated by the quality of the resulting radiances and retrieved profiles of temperature and trace species. The difficulties that have been eliminated, and that still remain are noted, along with plans for further improvement. Finally, the scientific implications are briefly discussed.
The High Resolution Dynamics Limb Sounder (HIRDLS) instrument was launched on the NASA Aura satellite in July 2004. HIRDLS is a joint project between the UK and USA, and is a mid-infrared limb emission sounder designed to measure the concentrations of trace species and aerosol, and temperature and pressure variations in the Earth's atmosphere between about 8 and 100 km. The instrument is performing correctly except for a problem with radiometric views out from the main aperture. A series of tests has led to the conclusion that optical beam is obstructed between the scan mirror and the aperture by what is believed to be a piece of Kapton film that became detached during the ascent to orbit. The paper describes measurements aimed at mapping the geometric and radiometric properties of the obstruction using different positions of the aperture door, including in some cases where the sun was made to illuminate the aperture. The aim of the work is to facilitate atmospheric observations through a small part of the aperture which remains clear.
A pre-launch calibration of the High Resolution Dynamics Limb Sounder (HIRDLS) flight instrument was performed at Oxford University in Fall 2002. The in-band spectral characterization was performed was performed as part of this exercise. Spectral response data for all 21 channels were obtained for three different experimental conditions (nominal and two off-nominal operating conditions). Results from these data sets will be presented, as well as the analysis procedures used, along with a discussion on error analysis.
The High Resolution Dynamics Limb Sounder (HIRDLS) flight
instrument, which is currently in orbit on the NASA Aura Satellite,
went through a pre-launch calibration at Oxford University during
Autumn 2002. One of the calibration exercises was to characterize the radiometric signals of the HIRDLS proto-flight model (PFM). It was discovered during the data-analysis phase, that the radiometric data required special treatment. Because of the stringent radiometric requirements imposed on HIRDLS, these additional analyses were necessary. This manuscript will detail these specific analysis techniques that were used on the data and present results based on a full analysis of the data, including a complete accounting of the statistical error analysis.
Carbon monoxide (CO) is an important tropospheric trace species and can serve as a useful tracer of atmospheric transport. The Measurements of Pollution In The Troposphere (MOPITT) instrument uses the 4.7 μm CO band to measure the spatial and temporal variation of the CO profile and total column amount in the troposphere from space. Launched in 1999 on board the NASA Terra satellite, the MOPITT views the earth with a pixel size 22 km by 22 km and a cross-track swath that measures a near-global distribution of CO every 3 days. In the operational MOPITT CO retrieval algorithm (V3; Version 3), surface skin temperature (Ts) and emissivity (E) are retrieved simultaneously with the CO profile. The accuracy of E and Ts is crucial for obtaining the CO retrieval within the 10% accuracy from the MOPITT measurements. However, because both Ts and E are retrieved from the same piece of information from the MOPITT measurements, the accuracy of both valuables may be limited. Extra surface skin temperature information is needed to determine surface emissivity, and vice versa. In this study, we use MODIS Ts within the MOPITT FOVs, in conjunction with those MOPITT signals most sensitive to the background scene, to compute the surface emissivity through an iterative retrieval algorithm. A monthly 1degree grid averaged 4.7 μm surface emissivity map is generated. The evaluation of the accuracy of this monthly 1 degree grid averaged 4.7 μm surface emissivity map is presented and its impacts on the retrievals of tropospheric CO profiles from the MOPITT measurements are also discussed.
The techniques used to calibrate the field of view of the High
Resolution Dynamics Limb Sounder (HIRDLS) instrument and the results
of the calibration are presented. HIRDLS will be flown on the NASA EOS
Aura platform. Both in-field and out-of-field calibrations were
performed. The calibration results are compared to the requirements
and, in the case of out-of-field, mechanisms explaining the results
are discussed.
Results from a pre-launch in-band spectral characterization of the 21-channel HIRDLS flight instrument will be presented. These data were obtained during a pre-launch calibration of HIRDLS at Oxford University (Fall 2002). A monochromator, equipped with a controllable diffraction grating, was used to produce monochromatic light for these tests. The monochromator was enclosed, with HIRDLS, in a large vacuum chamber. The monochromator was also equipped with a polarizer, which allowed for data to be procured at known orthogonal polarizations for each channel. A calibration detector, with a flat spectral response, was used to monitor the output from the monochromaotr. This report will consist of a description of the analyiss methodlogy, leading to an unpolarized instrument spectral response function for each channel.
The High Resolution Dynamics Limb Sounder (HIRDLS) instrument is scheduled for launch on the NASA AURA satellite in January 2004; it is a joint project between the UK and USA. HIRDLS is a mid-infrared limb emission sounder which will measure the concentration of trace species and aerosol, and temperature and pressure variations in the Earth's atmosphere between about 8 and 100 km altitude on a finer spatial scale than been achieved before. HIRDLS has particularly stringent radiometric calibration accuracy requirements. A warm (280-300K) 'In-Flight Calibrator' (IFC) black cavity within the instrument plus a view to cold space are used to perform radiometric calibration. The cavity has an entrance aperture which is much smaller than the full beam size, and it is viewed through a focusing mirror. The cavity and focusing mirror are ideally maintained at the same temperature but differences of up to 1 C may exist, in which case a correction utilising the mirror emissivity can usefully be made. That emissivity has been measured at instrument level during pre-launch calibration by viewing an external target at the same temperature as the IFC while varying the calibration mirror temperature.
The High Resolution Dynamics Limb Sounder (HIRDLS) Science Investigator-led Processing System (SIPS) is a software framework designed for operational, event-driven, instrument data processing. At its foundation are multiple open-source components that are assembled into a distributed architecture. The framework allows creation and modification of a wide array of processor and product scenarios. Java is used as the primary software language though processors can be implemented with any technology supported on the target platform. The software development approach, design and implementation technology are described along with several features and benefits of the system.
The High Resolution Dynamics Limb Sounder (HIRDLS) instrument is scheduled for launch on the NASA AURA satellite in January 2004; it is a joint project between the UK and USA. HIRDLS is a mid-infrared limb emission sounder which will measure the concentration of trace species and aerosol, and temperature and pressure variations in the Earth's atmosphere between about 8 and 100 km altitude on a finer spatial scale than has been achieved before. This will depend upon both a high quality of instrument build, and very precise pre-launch calibration. Proto Flight Model calibration was performed in a purpose-built laboratory at Oxford University during an 13-week period in 2002. The tests were made in vacuum under cryogenic conditions close to the space environment. The measurements were divided into spectral, spatial and radiometric, with the HIRDLS pointing capability being used to control which item of test equipment was viewed. A large degree of automation was achieved, and this combined with 24-hour/7-day working enabled a large quantity of information to be obtained.
Results from a pre-launch radiometric calibration of the 21-channel HIRDLS instrument will be presented. These data were obtained during a pre-launch calibration of HIRDLS at Oxford University (Fall 2002). Two external blackbody cavities were used to generate temperatures between ~90 K to ~320 K. These blackbodies were located, along with HIRDLS, inside a large vacuum chamber. Data were taken at three different focal-plane temperatures (61 K, 66 K, and 71 K). This paper will cover a variety of details; such as, data--taking procedures, analysis methodology, and the resulting linearity analyses.
Space-based experiments have contributed much to our knowledge of the stratosphere in recent years. These observations have been characterized by large horizontal or vertical scales, leaving a range of unobserved phenomena at smaller scales. This is especially true at the tropopause, the boundary between the troposphere and stratosphere, where rapid changes in the vertical in temperature and composition have been unobserved on a global basis. The HIRDLS instrument has been designed to address these issues. HIRDLS is a 21 channel limb scanning infrared radiometer designed to make global measurements at smaller vertical and horizontal scales than have been previously observed, from pole to pole, at altitudes of 8-80 km.
This paper will present an overview of the HIRDLS science and instrument, as well as the data retrieval process. It will serve as an introduction to the series of subsequent papers dealing with the calibration and other aspects of the experiment.
The MOPITT (Measurements of Pollution in the Troposphere) Airborne Test Radiometer (MATR) uses gas filter correlation radiometry from high altitude aircraft to measure tropospheric carbon monoxide. This is in support of the ongoing validation campaign for the MOPITT instrument on board the Tera Satellite. This paper reports on a recent study of MATR CO retrievals using observations of thermal radiation during the autumn of 2001 in western United States. Retrievals of CO were performed and compared to in-situ sampling with less than 7% retrieval error relative to the in-situ total column amount. The effects that influence the retrieval such as the instrument sensitivity, the retrieval sensitivity, and bias between observations and the radiation model are discussed.
The Measurements of Pollution In The Troposphere (MOPITT) instrument is designed to measure the spatial and temporal variation of the carbon monoxide (CO) profile and total column amount in the troposphere from the space. MOPITT channels are sensitive to both thermal emission from the surface and target gas absorption and emission. Surface temperature and emissivity are retrieved simultaneously with the CO profile. To obtain the desired 10% precision for the retrieved CO from MOPITT measurements, it is important to understand MOPITT CO channel sensitivity to surface temperature and emissivity and the impacts of the effects of any errors in retrieved skin temperature and emissivity on retrieved CO for various underlying surfaces. To demonstrate the impacts of the surface temperature and emissivity on the retrieval of the tropospheric CO profile, simulation studies are performed. The collocated Moderate Resolution Imaging Spectroradiometer (MODIS) surface products are used to assess the accuracy of the retrieved MOPITT surface temperature and emissivity.
The measurements of Pollution in the Troposphere (MOPITT) instrument aboard the Earth Observing System (EOS) Terra spacecraft measures tropospheric CO and CH4 by use of a nadir-viewing geometry. MOPITT cloud algorithm detects and removes measurements contaminated by clouds before retrieving CO profiles and CO and CH4 total columns. The collocation between MOPITT and MODIS is also established and MODIS cloud mask will be used in the MOPITT cloud algorithm. The cloud detection results in the use of MOPITT data alone agree with MODIS cloud mask for more than 80% of the tested cases.
The Measurements Of Pollution In The Troposphere (MOPITT) experiment will measure the amount of methane and carbon monoxide in the Earth's atmosphere utilizing spectroscopy in the near Infrared (IR) (2.2, 2.3, and 4.7 micrometer). In this wavelength region, clouds confound the retrieval of methane and carbon monoxide by shielding both the surface and atmospheric emission below the clouds from MOPITT. A technique has been developed to detect cloudy pixels, and an algorithm has been developed to estimate clear sky radiance from cloud contaminated pixels. This process is validated using images from the MODIS Airborne Simulator (MAS). MAS images are comprised of 50 m pixels in comparison to the larger 22 km MOPITT pixels. We aggregate the higher resolution MAS data to simulate MOPITT pixels. The aggregation is analyzed for clear and cloudy conditions and a cloud fraction is calculated. The aggregate is then averaged to recreate the scene that MOPITT would have seen. The cloud detection algorithms are applied to the degraded MAS image. The results are compared to validate the techniques imbedded in the standard MOPITT processing stream.
The Measurements Of Pollution In The Troposphere (MOPITT) instrument will monitor the global concentrations of carbon monoxide and methane. It will be flown on the Earth Observing Satellite, Terra (EOS-AM1), scheduled for launch late in 1999. This paper describes the proposed early mission operations of MOPITT.
Tropospheric concentrations of methane have been increasing at a rate of approximately 1%/year, though recent measurements suggest some slowing in this trend. Increased concentrations of methane, a greenhouse gas, will have significant consequences for tropospheric chemistry and climate on a global scale. Characterization of the spatial and temporal variability of methane is one goal of the MOPITT (Measurement of Pollution In The Troposphere) instrument included on the EOS Terra satellite. This instrument includes spectral channels designed to measure methane total column with approximately 1% precision with a spatial resolution of approximately 22 X 22 km. Retrieval of the methane total column will be accomplished by the MOPITT instrument from measurements of solar radiation reflected at the earth's surface. Gas correlation radiometry will be used to separate the spectral signature of methane in the upwelling radiance from features produced by other trace gases. The retrieval algorithm is based on maximum likelihood and uses an initial guess profile and methane total column variance estimates provided by aircraft in-situ measurements. In this talk, we will describe features of the retrieval algorithm in detail and present results of retrieval simulations conducted to test the sensitivity of the retrieval algorithm to various sources of error.
The Measurement Of Pollution In The Troposphere (MOPITT) instrument, which will be launched on the Terra spacecraft, is designed to measure the tropospheric CO and CH4 at a nadir-viewing geometry. The measurements are taken at 4.7 micrometer in the thermal region, and 2.3 and 2.2 micrometer in the solar region for CO mixing ratio retrieval, CO total column amount and CH4 column amount retrieval, respectively. To ensure the required measurement accuracy, it is critical to identify and remove any cloud contamination to the channel signals. In this study, we develop an algorithm to detect the cloudy pixels, to reconstruct clear column radiance for pixels with partial cloud covers, and to estimate equivalent cloud top positions under overcast conditions to enable CO profile retrievals above clouds. The MOPITT channel radiances, as well as the first guess calculations, are simulated using a fast forward model with input atmospheric profiles from ancillary data sets. The precision of the retrieved CO profiles and total column amounts in cloudy atmospheres is within the expected plus or minus 10% range. Validations of the cloud detecting thresholds with MODIS Airborne Simulator (MAS) data and MATR (MOPITT Airborne Test Radiometer) measurements are also carried out and will be presented separately.
The MOPITT (Measurement of Pollution in the Troposphere) instrument, to be launched on the Earth Observing System Terra platform, employs gas-correlation spectroscopy to measure profiles of tropospheric carbon monoxide and the total column of methane. The modeling of the instrument, and the associated radiative transfer, comprise the forward model employed in the retrieval calculations. The MOPITT forward model has been implemented through a hierarchy of radiation codes whose salient features are reviewed here.
This paper will serve as an overview of the challenges to the recovery of information on atmospheric CO and CH4 from the measurements made by the MOPITT instrument that has been described by Drummond et al. It will also provide a context and introduction to several of the following papers that go into greater detail on particular topics, and outline plans for the data processing. Here we briefly outline the principles of correlation radiometry as used by MOPITT, and introduce the principles behind the retrievals. After noting plans for data processing, we discuss our approach to data validation, and the ability to see global distributions of CO in the MOPITT data.
The Measurement of Pollution in the troposphere (MOPITT) instrument is an eight-channel gas correlation radiometer to be launched on the Earth Observing System (EOS) Terra spacecraft in 1999. Its main measurement objectives are tropospheric carbon monoxide (CO) profiles and total column. This paper gives a detailed description of MOPITT CO retrieval algorithm, which derives total CO column and tropospheric CO mixing ratios at a number of atmospheric pressure levels from MOPITT radiance observations. Retrieval performance evaluation using simulated MOPITT data are discussed.
We describe the top level design of the High Resolution Dynamics Limb Sounder (HIRDLS) instrument including the optical and scanning subsystems which have been developed to meet 0.7 arcsec pointing and the 1% radiometric accuracy requirements. The HIRDLS instrument is an infrared limb- sounding radiometer designed to sound the upper troposphere, stratosphere, and mesosphere. The instrument performs high resolution limb scans at multiple azimuth angles, measuring infrared emissions in 21 spectral channels ranging from 6 to 18 microns. The instrument design includes an off-axis Gregorian telescope with high resolution optical shaft encoders, a silicon carbide scanning mirror, and a vibration isolation system incorporating accelerometers in a feed- forward scanning control system. The detector subsystem includes 21 HgCdTe detector elements cooled by a mechanical Stirling cycle cooler.
We describe a radiometric model developed to simulate the transfer of time-dependent radiant and electrical signals through the High Resolution Dynamics Limb Sounder (HIRDLS). HIRDLS is an infrared limb-scanning satellite radiometer with 21 spectral channels defined by individual narrow band interference filters covering the spectral range from 6 to 18 micrometer. HIRDLS is scheduled to fly onboard the NASA Earth Observing System Chemistry platform to be launched early in the next century. The scientific objectives for HIRDLS place demanding requirements on instrument calibration and radiometric stability, particularly at low signal levels. The HIRDLS Radiometric Model (HIRAM) was developed to provide an analysis tool for evaluating the radiometric sensitivity to various subsystem parameters and observational conditions in support of requirements analyses and conceptual design studies. Instrument characteristics are modeled using analytic expressions where appropriate. HIRAM incorporates the results of detailed design and performance analyses conducted elsewhere (e.g. APART straylight analyses) as input parameters to the model. Random effects, such as detector noise, are generally modeled as band-limited white Gaussian noise. Where spectral dependence is important, such as modeling random line-of-sight jitter, a power spectral density function is used to define the frequency content of a random error source.
The High Resolution Dynamics Limb Sounder (HIRDLS) instrument is being built jointly by the UK and USA, and is scheduled for launch on the NASA EOS Chem satellite in 2002. HIRDLS will measure the concentration of trace species and aerosol, and temperature and pressure variations in the Earth's atmosphere between about 8 and 100 km altitude. It is an infrared limb emission sounder, and a primary aim is that it should measure to much finder spatial resolution than has previously been achieved, with simultaneous 1 km vertical and 500 km horizontal resolutions, globally, every 12 hours. Achieving these objectives will depend upon very precise pre-launch calibration. This will be undertaken at Oxford University in a test laboratory that is currently being constructed specifically for the task. The instrument will be surrounded by cryogenically cooled walls, and mounted together with the test equipment on an optical table contained in a vacuum chamber. The table will be mounted independently of the chamber, on an inertial mass supported on pneumatic isolators. Test equipment is being manufactured to measure (1) the radiometric response (with an absolute accuracy equivalent to 70 mK) using full aperture black body targets, (2) the spectral response of each of the filter channels using a grating monochromator, (3) the spatial response of the instrument field of view, including low level out-of-field contributions, to 10 (mu) rad accuracy using a monochromator. The methods and equipment used are described together with the principal requirements.
The Interferometric Monitor for Greenhouse Gases (IMG) uses Fourier transform spectrometry to measure the top of the atmosphere spectral radiance between 3.3 μm and 14 μm in 3 separate bands. It was launched aboard the Japanese ADEOS satellite in August 1996, and has an unapodized spectral resolution of 0.05 cm-1. IMG spectral radiance measurements over different geographical spectral resolution of 0.05 cm-1. IMG spectral radiance measurements over different geographical regions are compared with standard line-by-line radiative transfer model calculations. CO retrieval and comparison between synthetic spectra calculated by FASCOD3 and IMG observations during the WINter Clouds Experiment (WINCE) are discussed as a case study. Preliminary analysis indicates that the retrieved CO from IMG spectral radiance measurements agrees with in-situ measurements made by the Climate Monitoring and Diagnostics Laboratory of the National Oceanic and Atmospheric Administration (NOAA/CMDL) at the nearby Park Falls monitoring site.
The measurement of pollution in the troposphere (MOPITT) is an eight-channel gas correlation radiometer to be launched on EOS/AM1 spacecraft in 1999. The goal of the experiment is to support studies of the oxidizing capacity of the lower atmosphere on large scales by measuring the global distributions of carbon monoxide (CO) and methane and thus, will represent a significant advancement in the application of space based remote sensing to global tropospheric chemistry research. Validation of data processing algorithms and products is an essential component of the MOPITT project. Strategies and techniques to verify MOPITT measurement precision, accuracy, and resolutions will be described. Correlative measurements for MOPITT algorithm and data validation include measurements will be described. Correlative measurements for MOPITT algorithm and data validation include measurements by airborne remote sensing and in-situ techniques and ground-based spectroscopic techniques. The MOPITT data processing algorithms are being tested and validated using existing airborne and satellite observations before launch. Pre-launch validation campaigns have been conducted to intercompare different correlative measurement techniques and associated data processing algorithms.
This paper presents the application of discrete-point forward-backward Kalman filtering to improve pointing knowledge of the High Resolution Dynamics Limb Sounder (HIRDLS). The instrument is modeled by the following four sections: baseplate, optical bench 1, optical bench 2, and scanner plate. In this system, it is necessary to determine the pointing direction of the scanner with high accuracy. For this purpose, a gyro is affixed to the sounder on optical bench 2. The S/C attitude, extracted from a star- tracker and a second gyro, is also used in this determination. A final piece of information for determining HIRDLS pointing direction is available from the geopotential height at the equator; it has been shown that equatorial geopotential heights are relatively stable, and HIRDLS azimuth scanning is designed to overlap at eh equatorial region so that the same part of the atmosphere will be observed over two consecutive orbits. This condition allows determination of the instrument gyro drift at certain times in each orbit. To take advantage of this information, along with all other data from the various instruments, a discrete-point forward-backward Kalman filter is used to maximize pointing knowledge of the limb sounder. Computer simulation results are provided demonstrating the gains in pointing knowledge.
KEYWORDS: Carbon monoxide, 3D modeling, In situ metrology, Radiometry, Solar radiation models, Algorithm development, Troposphere, Statistical modeling, Atmospheric modeling, Signal to noise ratio
We have developed a retrieval algorithm for deriving the tropospheric CO profile and column amount from the radiances measured by the Measurements of Pollution in the troposphere instrument. The main components of the algorithm are a fast radiative transfer model, based on the GENLN2 line-by-line model, and a maximum likelihood inversion method. The retrieval a priori information is derived from the results of several aircraft in situ measurements and a 3D chemical- transport model. This paper discusses the CO retrieval algorithm with an emphasis on the analysis and characterization of the algorithm. Forward model and retrieval sensitivities, along with the a priori information used in the retrieval are discussed in terms of their orthogonal components. Examples of ensemble retrieval experiments are also included.
Two approaches have been explored for the retrieval of atmospheric constituent and aerosol extinction profiles from radiance measurements made by a limb sounding satellite radiometer. One of the retrieval schemes can be used with different signal to noise ratios and with measurements from different spectral regions. Multiple constituents can be retrieved simultaneously. Characterization and error analysis of the retrieved products arise naturally from theoretical considerations. The algorithms have been implemented on CLAES, an infrared limb sounder on the upper atmospheric research satellite. The CLAES measurement technique requires the level 1 extracted radiance data from CLAES to be processed before they are input to the NCAR research retrieval algorithm. The algorithms are applied to blocker 3 radiance measurements and some initial results are presented.
The scientific objectives and requirements for HIRDLS are presented, and the ways in which these flow down to some of the most important instrument requirements are shown. An overview of the conceptual design of the HIRDLS instrument, a 21-channel infrared limb scanner is presented, followed by a brief summary of the key requirements on the 9 subsystems, and an outline of some of their noteworthy design features.
The Measurements of Pollution in the Troposphere (MOPJTF) instrument is a
spaceborne gas correlation radiometer designed to measure CO and CH4 in the
troposphere. This instrument has been selected to be on board of the Earth Observing
System's first platform, EOS-AM, which is scheduled for launch in 1998. A maximum
likelihood retrieval algorithm has been selected for the MOPITT CO measurement in
clear sky conditions. Performance of the algorithm has been evaluated. This paper
describes the algorithm and presents the preliminary results of numerical retrieval
experiments.
In this paper we describe the scientific design work behind the selection of the IR spectral passbands for the 21 sounding channels of the high resolution dynamics limb sounder (HIRDLS) which is scheduled to fly aboard the Earth Observing System (EOS) chemistry platform at the beginning of the next century. At least one radiometer channel must be used for each gas that is being measured. Preferably the interfering contributions to the radiance by other gases in a channel should be small, but the principle requirements are that the desired emission be measured with high signal-to-noise ratio, and that there be separate channels for the measurement of interfering species. However, more than one channel is required to provide full altitude coverage of those target gases such as CO2, H2O, and O3, which have emission bands whose centers become optically thick in the middle atmosphere. Further channels, in which gaseous absorption is low, are required for the characterization of aerosol effects. We describe the HIRDLS channels selected for each gas, with emphasis on signal-to-noise considerations and altitude coverage, the elimination of contaminating signal between channels, and non-LTE processes for high altitude sounding and space view definition.
The HIRDLS instrument is being designed to obtain data to address critical questions related to the middle atmosphere and its role in global change. We briefly state the scientific objectives of the experiment, and then describe the requirements placed on the instrument. These include the ability to obtain measurements with 4 degree(s)latitudinal and longitudinal resolution, and 1 km vertical resolution, the ability to sound down into the upper troposphere when clouds are absent, and the ability to measure radiance profiles in order to infer temperature and the concentrations of a number of trace species of different chemical lifetimes, along with the gradients of the geopotential height fields, for 5 or more years. The HIRDLS instrument is a multichannel infrared limb scanner that significantly extends the measurement capabilities of earlier instruments such as LIMS and ISAMS. Advances include the use of a two-axis scanner to allow limb scans at multiple azimuths, narrow fields of view coupled with over-sampling, digital filtering and low noise to enhance vertical resolution, the use of larger numbers of channels to acquire data over a larger range of altitudes and the use of a gyroscope to determine motions of the optical bench. The ways in which this is done are described. The most demanding requirements are for radiometric accuracy and precision, and for precise pointing knowledge (in the presence of vibration). The results of trade-off studies are presented, and the current conceptual design is described.
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