Joel Susskind

AIRS/AMSU/HSB on the Aqua mission: design, science objectives, data products, and processing systems

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 Administrations 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 Administrations 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.

Retrieval of atmospheric and surface parameters from AIRS/AMSU/HSB data in the presence of clouds

New state-of-the-art methodology is described to analyze the Atmospheric Infrared Sounder/Advanced Microwave Sounding Unit/Humidity Sounder for Brazil (AIRS/AMSU/HSB) data in the presence of multiple cloud formations. The methodology forms the basis for the AIRS Science Team algorithm, which will be used to analyze AIRS/AMSU/HSB data on the Earth Observing System Aqua platform. The cloud-clearing methodology requires no knowledge of the spectral properties of the clouds. The basic retrieval methodology is general and extracts the maximum information from the radiances, consistent with the channel noise covariance matrix. The retrieval methodology minimizes the dependence of the solution on the first-guess field and the first-guess error characteristics. Results are shown for AIRS Science Team simulation studies with multiple cloud formations. These simulation studies imply that clear column radiances can be reconstructed under partial cloud cover with an accuracy comparable to single spot channel noise in the temperature and water vapor sounding regions; temperature soundings can be produced under partial cloud cover with RMS errors on the order of, or better than, 1 K in 1-km-thick layers from the surface to 700 mb, 1-km layers from 700-300 mb, 3-km layers from 300-30 mb, and 5-km layers from 30-1 mb; and moisture profiles can be obtained with an accuracy better than 20% absolute errors in 1-km layers from the surface to nearly 200 mb.

AIRS: Improving Weather Forecasting and Providing New Data on Greenhouse Gases

Abstract The Atmospheric Infrared Sounder (AIRS) and its two companion microwave sounders, AMSU and HSB were launched into polar orbit onboard the NASA Aqua Satellite in May 2002. NASA required the sounding system to provide high-quality research data for climate studies and to meet NOAAs requirements for improving operational weather forecasting. The NOAA requirement translated into global retrieval of temperature and humidity profiles with accuracies approaching those of radiosondes. AIRS also provides new measurements of several greenhouse gases, such as CO2, CO, CH4, O3, SO2, and aerosols. The assimilation of AIRS data into operational weather forecasting has already demonstrated significant improvements in global forecast skill. At NOAA/NCEP, the improvement in the forecast skill achieved at 6 days is equivalent to gaining an extension of forecast capability of six hours. This improvement is quite significant when compared to other forecast improvements over the last decade. In addition to NCEP, ECM...

Characteristics of the TOVS Pathfinder Path A dataset

Abstract The TIROS (Television Infrared Observation Satellite) Operational Vertical Sounder (TOVS) Pathfinder Path A dataset is currently a 9-yr dataset, 1985–93, of global fields of surface and atmospheric parameters derived from analysis of HIRS2 and MSU data on the NOAA-9, NOAA-10, NOAA-11, and NOAA-12 polar-orbiting operational meteorological satellites. The retrieved fields include land and ocean surface skin temperature, atmospheric temperature and water vapor profiles, total atmospheric O3 burden, cloud-top pressure and radiatively effective fractional cloud cover, outgoing longwave radiation (OLR) and longwave cloud radiative forcing, and precipitation estimate. The fields are gridded on a 1° × 1° latitude–longitude grid and stored on a 1-day mean, 5-day mean, and monthly mean basis, with data from each satellites local a.m. and p.m. orbits stored separately. Preliminary validation studies of the interannual differences of geophysical parameters derived from the TOVS Pathfinder dataset imply suff...

Improved Temperature Sounding and Quality Control Methodology Using AIRS/AMSU Data: The AIRS Science Team Version 5 Retrieval Algorithm

This paper describes the Atmospheric Infrared Sounder (AIRS) Science Team Version 5 retrieval algorithm in terms of its three most significant improvements over the methodology used in the AIRS Science Team Version 4 retrieval algorithm: the use of AIRS clear-column radiances in the entire 4.3-μm CO2 absorption band in the retrieval of temperature profiles T(p) during both day and night, with tropospheric sound ing of 15-μm CO2 observations now being used primarily in the generation of clear-column radiances R̂i for all channels; development of a new methodology to provide accurate case-by-case error estimates for retrieved geophysical parameters and for channel-by-channel clear column radiances and their use in a new approach for quality control; and an approach to provide AIRS soundings in partially cloudy conditions that does not require use of any microwave data. This new AIRS-only sounding methodology, referred to as AIRS Version 5 AO, was developed as a backup to AIRS Version 5 should the Advanced Microwave Sounding Unit (AMSU)-A instrument fail. Results are shown that compare the relative performance of the AIRS Version 4, Version 5, and Version 5 AO. Results using Version 5 retrievals in conjunction with different quality control thresholds are also shown for a recent period to demonstrate that empirical coefficients continue to be applicable in later time periods. The Goddard Data and Information Services Center (DISC) is now generating and distributing products derived using the AIRS Science Team Version 5 retrieval algorithm. This paper describes the quality control flags contained in the DISC AIRS/AMSU retrieval products and their intended use for scientific purposes.

Improved methodology for surface and atmospheric soundings, error estimates, and quality control procedures: the atmospheric infrared sounder science team version-6 retrieval algorithm

Abstract The atmospheric infrared sounder (AIRS) science team version-6 AIRS/advanced microwave sounding unit (AMSU) retrieval algorithm is now operational at the Goddard Data and Information Services Center (DISC). AIRS version-6 level-2 products are generated near real time at the Goddard DISC and all level-2 and level-3 products are available starting from September 2002. Some of the significant improvements in retrieval methodology contained in the version-6 retrieval algorithm compared to that previously used in version-5 are described. In particular, the AIRS science team made major improvements with regard to the algorithms used to (1) derive surface skin temperature and surface spectral emissivity; (2) generate the initial state used to start the cloud clearing and retrieval procedures; and (3) derive error estimates and use them for quality control. Significant improvements have also been made in the generation of cloud parameters. In addition to the basic AIRS/AMSU mode, version-6 also operates in an AIRS only (AO) mode, which produces results almost as good as those of the full AIRS/AMSU mode. The improvements of some AIRS version-6 and version-6 AO products compared to those obtained using version-5 are also demonstrated.

A biophysical process-based estimate of global land surface evaporation using satellite and ancillary data II. Regional and global patterns of seasonal and annual variations

A process-based biophysical model of evaporation described previously was run using spatially representative data to calculate global fields of monthly total transpiration, soil evaporation and interception for a period of 24 months (January 1987 to December 1988). Solution of the energy balance equation provided net radiation and sensible heat flux, complementing the evaporative flux. The zonally averaged (area weighted 5° latitude bands) values of annual total evaporation and evaporative fraction (ratio of evaporation and net radiation) are in broad agreement with previous estimates. Transpiration was found to be the dominant component of annual total evaporation in 20 out of the 28 latitude bands. Partitioning of annual total evaporation over the global land area is calculated to be, 52% transpiration, 28% soil evaporation and 20% interception. Seasonal variations of total evaporation and its components are presented for some specific types of vegetation (e.g., tundra, taiga, rainforest, crop land) and compared with field observations.

Diode laser spectra of the torsional splittings in the ν9 band of ethane: Torsion‐vibration‐rotation interactions and the barrier to internal rotation

Diode laser spectra of most of the Q branches of the ν9 band of ethane from RQ8–PQ15 have been recorded. The Q branches RQ0–RQ4 were deconvoluted to yield an effective resolution of (0.5–1.0)×10−3 cm−1 FWHM. Torsional splittings were observed for most lines. In contrast to predictions based on first order theory, the splittings which range from (2–53)×10−3 cm−1, have a marked J and K dependence. A second order theory of torsion‐vibration‐rotation interaction between ν9 and 3ν4 is developed, which fits the splittings with an rms error of 0.0006 cm−1, using only three adjustable parameters: the barrier to internal rotation in ν9, the energy difference between ν9 and 3ν4, and an effective coupling constant. The barrier to internal rotation in ν9 is found to be 1123±10 cm−1.

Synthetic atmospheric transmittance spectra near 15 and 4.3μm

Abstract Synthetic monochromatic atmospheric transmittance spectra are presented for infrared intervals in the vicinity of the 15 and 4.3μm CO2 bands. The intervals are nominally 20 cm-1 in width, and the spectra partition the intervals [560, 780] cm-1 and [2180, 2400] cm-1, respectively. The spectra are for a vertical atmospheric path. A given spectrum is presented at that pressure for which the mean weighting function (-d Tau (P) ⧸d ln P) is a maximum. In order to indicate the molecular origin of the features in a given spectrum, separate spectra are also presented for those species which make center line contributions to the absorption over the interval. The transmittance model for the calculations is described. In addition to the representation of spectral features for intervals which comprise these two CO2 bands, the spectra afford a utility in the design of high precision satellite temperature radiometers.

Outgoing longwave radiation from the TOVS Pathfinder Path A data set

A new outgoing longwave radiation (OLR) and clear-sky outgoing longwave radiation (COLR) data set derived from the Goddard TIROS operational vertical sounder (TOVS) Pathfinder Path A retrievals is introduced. Comparisons of OLR and COLR from TOVS Path A and the Earth Radiation Budget Experiment (ERBE) have been carried out for the period February 1985 to May 1989. In the OLR comparison, advanced very high resolution radiometer (AVHRR) OLR has also been included. The mean OLR differences and standard deviations of the differences between TOVS and ERBE are, in general, within 5 W m−2. The differences AVHRR minus ERBE, and AVHRR minus TOVS OLR are close to −4 and −7 W m−2, respectively. However, over oceanic subtropical regions, AVHRR OLR differs by −8 to −12 W m−2 compared with the other two data sets. The differences of TOVS and ERBE COLR over most regions are within ±4 W m−2, with standard deviations of differences between 4 and 12 W m−2. The OLR and COLR data sets have larger discrepancies over snow/ice-covered polar regions. Interannual variability of the OLR and COLR are compared for 1986–1988 in terms of their monthly mean anomalies. The global mean monthly ERBE OLR and COLR anomalies have somewhat larger magnitudes (−3.0 to 1.5 and −2.0 to 1.0 W m−2, respectively) compared with the other data sets (−1.0 to 1.0 and −0.7 to 0.7 W m−2, respectively). Both sets of ERBE anomalies appear to be influenced by the change of satellite from NOAA 9 to NOAA 10. The results of this study indicate that TOVS Path A and ERBE OLR and COLR are of comparable accuracy. The TOVS Path A data set covers a substantially longer time period (1985–1998) than ERBE and would be very useful in climate research studies.