The high-spectral-resolution AIRS (Atmospheric InfraRed Sounder) instrument onboard the NASA (National Aeronautics and Space Administration) Earth Observing System (EOS)-Aqua satellite represents the most advanced sounding system in space and provides unprecedented wealth of highly accurate radiance measurements. This paper describes a standalone and fast single field-of-view (FOV) algorithm to retrieve atmospheric sounding profiles (temperature, humidity, ozone) and surface parameters (surface skin temperature, surface emissivity) from AIRS Level 1B (L1B) clear only infrared radiance measurements. The retrieval algorithm is part of the International MODIS (Moderate Resolution Imaging Spectroradiometer)/AIRS Processing Package (IMAPP) software package, which provides international users with the capability of receiving and processing direct broadcast data in real-time. The IMAPP AIRS retrieval algorithm is based on principal component regression to obtain fast and accurate estimates of the atmospheric state at single FOV. This algorithm is designed specifically for real-time direct broadcast applications where sounding products can be processed efficiently at highest possible spatial resolution. Simulated radiance data is trained on a global set of profiles, representative of a wide variety of atmospheric scenes, which makes the algorithm globally applicable. The results presented and discussed in this paper demonstrate that the IMAPP AIRS retrieval product is rigorously evaluated by various product sources such as numerical weather prediction model analysis fields, retrieved parameters from the operational AIRS L2 product and data from other instruments.
The Atmospheric Infrared Sounder (AIRS) onboard Aqua satellite is providing a wealth of highly accurate atmospheric
and surface information using 2378 high-spectral-resolution infrared (3.7 - 15.4 μ) channels. Cooperative Institute for
Meteorological Satellite Studies (CIMSS) has developed International MODIS/AIRS Processing Package (IMAPP) to
retrieve atmospheric and surface parameters from AIRS-L1B radiance measurements. CIMSS retrieval algorithm is
based on principal component regression technique. In order to account for retrieval dependency on zenith angle and
regional/seasonal variations a classification scheme is employed based on scan angle classification and window-channel
brightness temperature classification.
To improve atmospheric sounding retrieval for a specific region, which is useful for AIRS direct broadcast users,
regional regression coefficients have been generated for Indian region. Training dataset of radiosonde observations over
India and surrounding region have been used to generate regional regression coefficients for IMAPP-AIRS processing.
Retrieval error statistics was generated using simulated radiances from independent dataset of radiosonde observations
over Indian region. This study shows that the Root Mean Square (RMS) error in humidity profile is reduced by ~25%
when compared to the global regression coefficients, whereas RMS error for temperature profile is reduced by ~0.2 K.
This study is also useful for sounding retrieval from geostationary sounder measurements, for example, for
Geostationary Operational Environmental Satellite (GOES) Sounder and INSAT-3D Sounder that have observations
over a limited region with high spatial and temporal resolution.
Present study describes a methodology to establish an empirical expression to estimate the upper tropospheric humidity
(UTH) from brightness temperature observations in water vapour channel of Very High Resolution Radiometer (VHRR)
onboard Indian geostationary satellites INSAT-3A and Kalpana. Radiative transfer simulations for VHRR water vapour
channel were made using SBDART model for tropical atmosphere with different upper tropospheric relative humidity
values and varying zenith angles. INSAT-3A and Kalpana VHRR sensor response functions (SRF) for water vapour
channel were used to simulate the convolved radiances. Estimated UTH values have been compared with corresponding
Meteosat-5 observations. Comparison of retrieved UTH is also made with radiosonde observations of relative humidity
weighted by water vapour channel weighting function.
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