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The Atmospheric Infrared Sounder (AIRS) on the EOS Aqua Spacecraft was launched on May 4, 2002. AIRS acquires hyperspectral infrared radiances in the 3.7–15.4 μm spectral region with spectral resolving power of better than 1200. The AIRS was designed to measure temperature and water vapor profiles and cloud properties for improvement in weather forecast and improved parameterization of climate processes. Currently a subset of AIRS Level 1B Radiance Products is assimilated by NWP centers, resulting in significant forecast improvement. Scientists have also demonstrated accurate retrievals of minor gases from AIRS including carbon monoxide, methane, and ozone. The excellent sensitivity and stability of the AIRS instrument has recently allowed the AIRS team to successfully retrieve carbon dioxide (CO 2 ) concentrations in the mid-troposphere (8–10 km) with a horizontal resolution of 100 km and accuracy better than 2 ppm. The AIRS mid-tropospheric CO 2 yield is 15,000 measurements per 24-h period over land and ocean, day and night for clear and cloudy scenes. The AIRS CO 2 accuracy has been validated against a variety of mid-tropospheric aircraft measurements as well as upward looking interferometers. Findings from the AIRS data include higher than expected variability in the mid-troposphere, the presence of a seasonally variable belt of enhanced CO 2 in the southern hemisphere, and observations of impact of atmospheric dynamics on the CO 2 concentrations in the mid-troposphere including the effects of El Nino/La Nina and the Arctic polar vortex. The full mid-tropospheric AIRS CO 2 data set is now available at the NASA GES/DISC for the 8 year time span since AIRS became operational.

This paper discusses the performance of AIRS and examines how it is meeting its operational and research objectives based on the experience of more than 2 yr with AIRS data. We describe the science background and the performance of AIRS in terms of the accuracy and stability of its observed spectral radiances. We examine the validation of the retrieved temperature and water vapor profiles against collocated operational radiosondes, and then we assess the impact thereof on numerical weather forecasting of the assimilation of the AIRS spectra and the retrieved temperature. We close the paper with a discussion on the retrieval of several minor tropospheric constituents from AIRS spectra.

The Atmospheric Infrared Sounder (AIRS), the Advanced Microwave Sounding Unit (AMSU), and the Humidity Sounder for Brazil (HSB) form an integrated cross-track scanning temperature and humidity sounding system on the Aqua satellite of the Earth Observing System (EOS). AIRS is an infrared spectrometer/radiometer that covers the 3.7-15.4-/spl mu/m spectral range with 2378 spectral channels. AMSU is a 15-channel microwave radiometer operating between 23 and 89 GHz. HSB is a four-channel microwave radiometer that makes measurements between 150 and 190 GHz. In addition to supporting the National Aeronautics and Space Administration's interest in process study and climate research, AIRS is the first hyperspectral infrared radiometer designed to support the operational requirements for medium-range weather forecasting of the National Ocean and Atmospheric Administration's National Centers for Environmental Prediction (NCEP) and other numerical weather forecasting centers. AIRS, together with the AMSU and HSB microwave radiometers, will achieve global retrieval accuracy of better than 1 K in the lower troposphere under clear and partly cloudy conditions. This paper presents an overview of the science objectives, AIRS/AMSU/HSB data products, retrieval algorithms, and the ground-data processing concepts. The EOS Aqua was launched on May 4, 2002 from Vandenberg AFB, CA, into a 705-km-high, sun-synchronous orbit. Based on the excellent radiometric and spectral performance demonstrated by AIRS during prelaunch testing, which has by now been verified during on-orbit testing, we expect the assimilation of AIRS data into the numerical weather forecast to result in significant forecast range and reliability improvements.

The Atmospheric Infrared Sounder (AIRS) on the EOS Aqua Spacecraft was launched in May of 2002. The AIRS Sounding Suit, AIRS along with AMSU-A and HSB, were designed to measure the atmospheric temperature and water vapor profiles, the surface and the cloud parameters for climate research and for improvement in weather forecast. Over the last 8+ years AIRS has been operating extremely stable, far surpassing original design life of 4 - 5 years. Many exciting research papers on climate have been published with AIRS data. The AIRS data are assimilated by most NWP centers and have shown considerable improvement in forecast skill. We will describe the current status of the instruments as well as the new activity on the data processing software.

The Atmospheric Infrared Sounder (AIRS) on the EOS Aqua Spacecraft was launched on May 4, 2002. Early in the mission, the AIRS instrument demonstrated its value to the weather forecasting community with better than 6 hours of improvement on the 5 day forecast. Now with over eight years of consistent and stable data from AIRS, scientists are able to examine processes governing weather and climate and look at seasonal and interannual trends from the AIRS data with high statistical confidence. Naturally, long-term climate trends require a longer data set, but indications are that the Aqua spacecraft and the AIRS instrument should last beyond 2018. This paper briefly describes the AIRS data products and presents some of the most significant findings involving the use of AIRS data in the areas of weather forecast improvement, climate processes and model validation, cloud and polar processes, and atmospheric composition (chemistry and dust).

[1] Simple prototypes for forced advection-diffusion problems are known to produce passive tracer distributions that exhibit approximately exponential or stretched exponential tails. Having previously found an approximately exponential tail for the column integrated water vapor (CWV) distribution under high precipitation conditions, we conjectured that if such prototypes are relevant to more complex tropospheric tracer problems, we should find such tails for a wide set of tracers. Here it is shown that such tails are indeed ubiquitous in observed, model, and reanalysis data sets for a variety of tracers, either column integrated or averaged through a deep layer, including CO and CO2. The long tails in CWV are associated with vertical transport and can occur independent of a local precipitation sink. These non-Gaussian distributions can have consequences for source attribution studies of anthropogenic tracers, and for mechanisms of precipitation extremes; the properties of the tails may help constrain model tracer simulations.

The current theoretical and observational understanding of the roles of the hydrological cycle in the climate system and its intimate connection to the energy cycle is evaluated. An attempt is made to show why the hydrological cycle has emerged as the central element in studies of climate change and to anticipate the main advances expected in modeling and observations in the coming decade.

Accurate long-term global data sets are essential for achieving better understanding of the Earth's climate system and for modelling its complex interactions and feedback mechanisms. The High Resolution Infrared Sounder and the Microwave Sounding Unit (HIRS2/MSU) observations readily offer a unique opportunity to establish a global self-consistent data set of more than ten climate parameters extending over a decade in time. Such a data set would add considerably to our current information. To this end, we have developed and tested a retrieval package to extract geophysical parameters from the combination of infrared and microwave data returned since December 1978 from the NOAA weather satellites. The retrieval algorithm is an interactive forecast-retrieval-assimilation system based on the relaxation method of solution of the radiative transfer equation. The first guess is obtained from the six-hour forecast field generated by the General Circulation Model (GCM) of the Goddard Laboratory for Atmospheres. At present we have applied the algorithm to analyze the first two years of HIRS2/MSU data. The resulting climate data sets include: atmospheric temperature profiles, atmospheric humidity profiles, ocean surface temperature, land surface temperature, infrared cloud cover, cloud-top height and temperature, snow and ice cover, outgoing long-wave radiation, total ozone distribution, and rainfall rate index. We have conducted several tests to check the accuracy, internal consistency and stability of the results. Additional tests will be made in the future with this set as well as when multi-year data are derived.

Hyperspectral infrared atmospheric sounders (e.g. the Atmosphe ric Infrared Sounder (AIRS) on Aqua and the Infrared Atmospheric Sounding Interferometer (IAS I) 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 forecast 1 . Despite the success in the mid troposphere to lowe r 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. Improv ements are also expected in the accuracy of the water vapor and cloud properties products, enhanc ing 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. Keywords: Atmosphere, Sounder, Temperature, Water Vapor, Profile, Advanced

We apply the method of Vanishing Partial Derivatives (VPD) to AIRS spectra to retrieve daily the global distribution of CO2 at a nadir geospatial resolution of 90 km x 90 km without requiring a first-guess input beyond the global average. Our retrievals utilize the 15 (micro)m band radiances, a complex spectral region. This method may be of value in other applications, in which spectral signatures of multiple species are not well isolated spectrally from one another.

The Atmospheric Infrared Sounder (AIRS) on the EOS Aqua spacecraft provides calibrated radiances and geophysical products for Earth science investigation and validation of processes affecting weather and climate. A description of the major products including temperature profiles, water vapor profiles, surface products, cloud products and composition products is presented. The wide variety of products available from AIRS make it uniquely able to address science questions involving interaction of geophysical variables in the climate system.

The wide range of products available from AIRS have made it invaluable as a tool for operational weather forecasting and climate modeling. AIRS has improved the 5 day forecast by 6 hours in the NCEP operational system and researchers have identified further improvement potential by assimilation of more channels and footprints. AIRS data have been used to validate the distribution and transport of water vapor and greenhouse gases in climate models, resulting in the identification of significant errors in the handling of these quantities. We present the AIRS Version 5 products and their accuracies and reference key papers involving their use. We also touch briefly on the limitations of AIRS due to its coarse spatial resolution, particularly in achieving boundary layer sensitivity.

It is now possible to combine high spectral resolution observations (like AIRS) with moderate spatial resolution (like MODIS) in a single instrument. The ARIES instrument concept provides over 3000 spectral channels in the 0.4 - 15.4 μm spectral region with spatial resolution of 1.0 km while still scanning ±55°. The ARIES has size and mass less than half that of AIRS or MODIS primarily due to the advancements in focal plane assemblies and wide field optical systems developed under the NASA IIP and in US industry. The combined capability will allow more cloud free observations per unit area, and improve the overall cloud-clearing approach applied on AIRS. It will also improve sensitivity to atmospheric water vapor, temperature and trace gases in the boundary layer and facilitate studies of surface and atmospheric interaction for global climate studies. Improvements are expected in regional weather forecasts and hurricane prediction. This paper discusses the primary requirements for ARIES, the expected science and operational benefits and an instrument concept that demonstrates the viability and low risk of the approach.

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.

This paper presents the standard and research products from Atmospheric Infrared Sounder (AIRS) and their current accuracies as demonstrated through validation efforts. It also summarizes ongoing research using AIRS data for weather prediction and improving climate models.

We examine differences in total precipitable water vapor (PWV) from the Atmospheric Infrared Sounder (AIRS) and the Advanced Microwave Scanning Radiometer (AMSR-E) experiments sharing the Aqua spacecraft platform. Both systems provide estimates of PWV over water surfaces. We compare AIRS and AMSR-E PWV to constrain AIRS retrieval uncertainties as functions of AIRS retrieved infrared cloud fraction. PWV differences between the two instruments vary only weakly with infrared cloud fraction up to about 70%. Maps of AIRS-AMSR-E PWV differences vary with location and season. Observational biases, when both instruments observe identical scenes, are generally less than 5%. Exceptions are in cold air outbreaks where AIRS is biased moist by 10-20% or 10-60% (depending on retrieval processing) and at high latitudes in winter where AIRS is dry by 5-10%. Sampling biases, from different sampling characteristics of AIRS and AMSR-E, vary in sign and magnitude. AIRS sampling is dry by up to 30% in most high-latitude regions but moist by 5-15% in subtropical stratus cloud belts. Over the northwest Pacific, AIRS samples conditions more moist than AMSR-E by a much as 60%. We hypothesize that both wet and dry sampling biases are due to the effects of clouds on the AIRS retrieval methodology. The sign and magnitude of these biases depend upon the types of cloud present and on the relationship between clouds and PWV. These results for PWV imply that climatologies of height-resolved water vapor from AIRS must take into consideration local meteorological processes affecting AIRS sampling.

[1] AIRS was launched on EOS Aqua on 4 May 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 1 K, and layer precipitable water with an RMS error of 20%, in cases with up to 80% effective cloud cover. The basic theory used to analyze AIRS/AMSU/HSB data in the presence of clouds, called the at-launch algorithm, was described previously. Prelaunch simulation studies using this algorithm indicated that these results should be achievable. Some modifications have been made to the at-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 and the RMS accuracy of lower-tropospheric temperature retrieved with 80% cloud cover is about 0.5 K poorer than for clear cases. HSB failed in February 2003, and consequently, HSB channel radiances are not used in the results shown in this paper. The AIRS/AMSU retrieval algorithm described in this paper, called version 4, become operational at the Goddard DAAC (Distributed Active Archive Center) in April 2003 and is being used to analyze near-real time AIRS/AMSU data. Historical AIRS/AMSU data, going backward from March 2005 through September 2002, is also being analyzed by the DAAC using the version 4 algorithm.

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 P m to 15.4 P m. AIRS is unique in that it provides the highest infrared spectr al 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, California 1 . 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 weathe r forecasting and the studies of proce sses affecting climate and weather. KEYWORDS Remote Sensing, Infrared, Weather Forecasting, Humidity, Temperature Profiles, Greenhouse Gases

Determination of atmospheric carbon requires an unprecedented precision for a satellite sounding measurement. Simulation experiments are used to assess the relative performance of the trace gas retrievals from the NASA AIRS, METOP IASI and NPOESS CrIS instruments.

The Atmospheric Infrared Sounder (AIRS) was launched in May 2002. Along with two companion microwave sensors, it forms the AIRS Sounding Suite. This system is the most advanced atmospheric sounding system to date, with measurement accuracies far surpassing those available on current weather satellites. The data products are calibrated radiances from all three sensors and a number of derived geophysical parameters, including vertical temperature and humidity profiles, surface temperature, cloud fraction, cIoud top pressure, and profiles of ozone. These products are generated under cloudy as well as clear conditions. An ongoing calibration validation effort has confirmed that the system is very accurate and stable, and many of the geophysical parameters have been validated. AIRS is in some cases more accurate than any other source and can therefore be difficult to validate, but this offers interesting new research opportunities. The applications for the AIRS products range from numerical weather prediction to atmospheric research - where the AIRS water vapor products near the surface and in the mid to upper troposphere will make it possible to characterize and model phenomena that are key for short-term atmospheric processes, such as weather patterns, to long-term processes, such as interannual cycles (e.g., El Nino) and climate change.

The application of hyper spectral radiometric data to climate research requires very high absolute radiometric accuracy and stability. We use cloud-free tropical ocean data from the Atmospheric InfraRed Sounder (AIR) Calibration Data Subset (ADCS) to show that the radiometric precision and stability required climate applications has been achieved. The sea surface skin temperatures derived from the AIRS 2616cm-1 super window channel are stable relative to the RTG.SST at the better than 8 mK/year level, and the spectral calibration is stable at the 1 ppm/year level. The excellent stability and accuracy are the result of the implementation of AIRS as a grating array spectrometer, which is cooled and stabilized within 10 mK at 155 K. Analysis of daily measurements of the temperature gradient between the surface and 7 km altitude show that the AIRS Calibration Data Subset has applications which extend its original intent for calibration support to climate research. The Atmospheric Infrared Sounder (AIRS) on the EOS Aqua satellite was launched into polar orbit in May 2002. AIRS covers the spectral region from 640 to 2700 cm-1 with 2378 independent channels and represents the first of a new generation of hyper spectral resolution sounders in support of global sounding data for weather forecasting and climate research.

The AIRS instrument was launched on the Aqua satellite in May of 2002. In addition to the core level 2 products, that include cloud cleared radiances; temperature, moisture, and ozone profiles; surface skin temperature; NDVI (from AIRS visible channels); surface spectral emissivity and reflectivity; and cloud products, the AIRS science team is also developing research algorithms for the retrieval of carbon monoxide (CO), methane (CH 4 ), and carbon dioxide (CO 2 ). These algorithms are being tested by the National Oceanographic and Atmosphere Administration (NOAA) National Environmental Satellite, Data, and Information Service (NESDIS) in simulation and applied to real AIRS radiances. The trace gas retrievals require cloud free infrared radiances. In practice, we observe that AIRS measurements without cloud contamination occur less than 5% of the time. A key feature of the AIRS algorithm is the utilization of cloud cleared radiances that removes the effects of clouds and increases the yield of trace gas products to 50-60%. The increased yield should allow a better assessment of sources and sinks of these gases. Determination of sources and sinks of these trace gas requires an unprecedented precision for a remote sounding measurement. In addition, both the variability and errors in the trace gas products tend to be correlated with variability and errors in other products (e.g., clouds, temperature, moisture, and ozone profile). Multi-spectral, high-resolution measurements can minimize the effects of this correlation. Currently, for the AIRS products, we estimate a precision of 15% for CO, 0.5% for CO 2 and 1% for CH 4 . The remote sounding methodology for these trace gases is discussed in detail. The METOP IASI and NPOESS CrIS instruments can extend the continuity of these trace gas products over the next two decades. Simulation experiments are used to assess the relative performance of the trace gas retrievals from these sounders.

The Atmospheric Infrared Sounder (AIRS), Advanced Microwave Sounding Unit (AMSU), and Humidity Sounder from Brazil (HSB) are three instruments onboard the Earth Observing System (EOS) Aqua Spacecraft. Together, they form the Aqua Infrared and Microwave Sounding Suite (AIMSS). This paper discusses the science objectives and the status of the instruments and their data products one year after launch. All instruments went through a successful activation and calibration and have produced exceptional, calibrated, Level 1B data products. The Level 1B Product Generation Executables (PGEs) have been given to NOAA and the GSFC DAAC for production and distribution of data products. After nine months of operations, the HSB instrument experienced an electrical failure of the scanner. Despite the loss of HSB, early validation results have shown the AIRS and AMSU are producing very good temperature profiles.

The atmospheric infrared sounder (AIRS) is being developed for the NASA Earth Observing System (EOS) program with a scheduled launch on the first post meridian (PM) platform in the year 2000. AIRS is designed to provide both new and more accurate data about the atmosphere, land, and oceans for applications to climate studies and weather prediction. Among the important parameters to be derived from AIRS observations are atmospheric temperature profiles with an average accuracy of 1K in 1 kilometer (km) layers in the troposphere and surface temperatures with an average accuracy of 0.5 K. The AIRS measurement technique is based on very sensitive passive IR remote sensing using a precisely calibrated, high spectral resolution grating spectrometer operating in the 3.7 micrometers to 15.4 micrometers region. The instrument concept utilizes a passively cooled multiaperture echelle array spectrometer approach in combination with advanced state of the art focal plane and cryogenic refrigerator technology to achieve unparalleled performance capability in a practical long life configuration. AIRS is a key component of NASA's Global Change Research Program and is expected to play an important role in fulfilling the needs of the converged National Polar- Orbiting Operating Environment Satellite System (NPOESS) now under study. This paper provides a brief overview of the mission followed by a description of the instrument design and current development status.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

High spectral resolution infrared satellite data can be used to retrieve accurate atmospheric temperature and water vapor profiles. In order to achieve the greatest retrieval accuracy, all the factors affecting the radiances, especially clouds, must be accurately accounted for. We have developed a methodology for retrieving atmospheric and surface parameters under cloudy conditions using the AIRS/AMSU instruments. Since all fields-of-view are contaminated to some degree by clouds, the task of eliminating clouds must be analytical, objective, and accurate. This is accomplished with great success by making use of observations in adjacent fields-of-view utilizing both the microwave and infrared bands. The treatment of clouds is carried out systematically and does not require any field-of-view to be necessarily clear. The only assumption about cloudiness is that clouds have identical spectral properties in both fields-of-view. The algorithm permits the determination of atmospheric temperature and water vapor profiles accurately under cloudy conditions and shows little degredation in their accuracy as a function of increased cloudiness.

The accuracy of the hydrological cycle stated in the article is derived from the accuracy of its components. Globally, precipitation is poorly measured because of its high temporal and spatial variability. Simpson [1989] states “Most of the rain in the tropic falls in regions that are relatively inaccessible to in situ measurements. The quantitative distribution over the tropical oceans is uncertain to a multiplicative factor of about two to three.” In addition, our knowledge of global evaporation is also deficient. Soil moisture, plant evapotranspiration, and the fluxes of moisture from both the oceans and land are very difficult to measure and, on a global scale, are just as poorly known as precipitation. While atmospheric water vapor can be measured globally from space, its accuracy, according to Barnett et al. [1991], is known only to about 10–20% over the geographical oceans and 20–30% over land.

GEWEX, which is part of the World Climate Research Program, has as its goal an order-of-magnitude improvement in the ability to model global precipitation and evaporation and furnish an accurate assessment of the sensitivity of atmospheric radiation and clouds. Attention will also be given to the response of the hydrological cycle and water resources to climate change. GEWEX employs a single program to coordinate all aspects of climatology from model development to the deployment and operation of observational systems. GEWEX will operate over the next two decades.

Day and night mapping of the global distributions of the horizontal cloud covers and the corresponding cloud-top pressure levels are derived from the same set of infrared radiance data used to retrieve clear-column temperature profiles. General formulation of the problem is presented with illustrations for the simple case of a single layer of non-reflecting clouds. Experimental verification is obtained using 15 micron data measured by the NOAA-VTPR infrared sounder. After correcting for water vapor emission, the results show that the effective cloud cover derived from 15 micron data is less than that obtained from visible data.

Several important land, atmosphere, and ocean surface parameters are being derived from weather satellite data acquired by the High Resolution Infrared Sounder (HIRS) and the Microwave Sounding Unit (MSU). The parameters thus far derived from these two instruments correspond to the entire year 1979 and the months of March and July 1982. They include: atmospheric temperature and humidity profiles, ocean and land skin surface temperatures, cloud amount, cloud top pressure, temperature, and ice and snow cover. The numerical retrieval algorithm used is based on the iterative relaxation method, which is fundamentally different from statistically based methods. Rather than rely on empirical relationships between satellite observations and meteorological conditions, the relaxation approach finds the solution by iterating until the calculated outgoing radiances, obtained by substituting the iterative atmospheric and surface parameters into the radiative transfer equation, match the observations to a specified accuracy.

AMERICAN METEOROLOGICAL SOCIETY | 891 AFFILIATIONS : LE MARSHALL, JUNG, DERBER, TREADON, LORD, GOLDBERG, WOLF, LIU, JOINER, WOOLLEN, TODLING, VAN DELST, AND TAHARA—NASA, NOAA, and U.S. Department of Defense Joint Center for Satellite Data Assimilation, Camp Springs, Maryland; CHAHINE—NASA Jet Propulsion Laboratory, Pasadena, California CORRESPONDING AUTHOR: John Le Marshall, Joint Center for Satellite Data Assimilation, NOAA Science Center, 5200 Auth Road, Camp Springs, MD 20746 E-mail: John.Lemarshall@noaa.gov

The methods used to determine effective cloud fraction (cloud fraction times cloud emissivity at 11-14 microns) and cloud top pressure from analysis of HIRS2/MSU sounding data are described. Identical procedures are used day and night so as to allow for meaningful day-night difference fields. Results are shown for June 1979. The monthly mean effective cloud fraction is 43.4 percent, resulting from a 45.2 percent value at 0300 LT and 41.6 percent at 1500 LT. The retrieved single-day cloud field for June 11 shows good agreement with high spatial resolution visible and infrared imagery.

At the Goddard Laboratory for Atmospheric Sciences (GLAS) a physically based satellite temperature sounding retrieval system, involving the simultaneous analysis of HIRS2 and MSU sounding data, has been developed for determining atmospheric and surface conditions which are consistent with the observed radiances. In addition to determining accurate atmospheric temperature profiles even in the presence of cloud contamination, the system provides global estimates of day and night sea or land surface temperatures, snow and ice cover, and parameters related to cloud cover. The inverse radiative transfer equation approach to the multi-spectral analysis of the data, and details of its implementation, are described. Ice, snow, and cloud fields derived for January 1979 are consistent with other measures of similar parameters obtained from AVHRR and SMMR. Monthly mean sea-surface temperature fields agree with those derived from ship and buoy measurements to 0.5 C.