Atmospheric Radiation Measurement site atmospheric state best estimates for Atmospheric Infrared Sounder temperature and water vapor retrieval validation

Abstract

[1] The Atmospheric Infrared Sounder (AIRS) is the first of a new generation of advanced satellite-based atmospheric sounders with the capability of obtaining high-vertical resolution profiles of temperature and water vapor. The high-accuracy retrieval goals of AIRS (e.g., 1 K RMS in 1 km layers below 100 mbar for air temperature, 10% RMS in 2 km layers below 100 mbar for water vapor concentration), combined with the large temporal and spatial variability of the atmosphere and difficulties in making accurate measurements of the atmospheric state, necessitate careful and detailed validation using well-characterized ground-based sites. As part of ongoing AIRS Science Team efforts and a collaborative effort between the NASA Earth Observing System (EOS) project and the Department of Energy Atmospheric Radiation Measurement (ARM) program, data from various ARM and other observations are used to create best estimates of the atmospheric state at the Aqua overpass times. The resulting validation data set is an ensemble of temperature and water vapor profiles created from radiosondes launched at the approximate Aqua overpass times, interpolated to the exact overpass time using time continuous ground-based profiles, adjusted to account for spatial gradients within the Advanced Microwave Sounding Unit (AMSU) footprints, and supplemented with limited cloud observations. Estimates of the spectral surface infrared emissivity and local skin temperatures are also constructed. Relying on the developed ARM infrastructure and previous and ongoing characterization studies of the ARM measurements, the data set provides a good combination of statistics and accuracy which is essential for assessment of the advanced sounder products. Combined with the collocated AIRS observations, the products are being used to study observed minus calculated AIRS spectra, aimed at evaluation of the AIRS forward radiative transfer model, AIRS observed radiances, and temperature and water vapor profile retrievals. This paper provides an introduction to the ARM site best estimate validation products and characterizes the accuracy of the AIRS team version 4 atmospheric temperature and water vapor retrievals using the ARM products. The AIRS retrievals over tropical ocean are found to have very good accuracy for both temperature and water vapor, with RMS errors approaching the theoretical expectation for clear sky conditions, while retrievals over a midlatitude land site have poorer performance. The results demonstrate the importance of using specialized ''truth'' sites for accurate assessment of the advanced sounder performance and motivate the continued refinement of the AIRS science team retrieval algorithm, particularly for retrievals over land.

A 6-year global cloud climatology from the Atmospheric InfraRed Sounder AIRS and a statistical analysis in synergy with CALIPSO and CloudSat

“…The proximity recognition between the AIRS L2 atmospheric profiles and the TIGR atmospheric profiles is described in detail in . If no simultaneous AIRS L2 atmospheric profile of good quality is available (which may occur if the situation is too cloudy), a running mean average of atmospheric profiles with good quality (Tobin et al, 2006) over one week, at a spatial resolution of 1 • latitude×1 • longitude, is used. The third choice is a monthly mean of atmospheric profiles with good quality, at 1 • latitude×1 • longitude.…”

“…These atmospheric profiles were retrieved from cloud-cleared AIRS radiances within each AMSU footprint. Validations with radiosonde data from the NOAA-NESDIS operational meteorological database archive (Divakarla et al, 2006) and with Atmospheric Radiation Measurement (ARM) data (Tobin et al, 2006) have shown that the accuracy is close to 1 K in 1 km layers for temperature and better than 15% in 2 km layers for water vapour. For the cloud property retrieval we have collocated the AIRS L2 standard products (version 5) with a subset of AIRS L1B radiance measurements which have been downloaded from the NASA data pool (http://mirador.gsfc.nasa.gov).…”

Validation assessment model for atmospheric retrievals

“…We applied the VAM to a set of radiosonde profiles taken at the ARM Southern Great Plains site from July to December of 2002. These are the same data that have been used to build the "best estimate data set" in Tobin et al 6 . In particular, we analyzed the impact of the time difference between satellite and radiosonde measurements on the assessment of accuracy of the AVTP retrieval.…”

“…In practice two approaches are used to handle the issue of non-collocation 5 . Thus, in the work of Tobin et al 6 the "best estimate" radiosonde data set for the Southern Great Plains ARM site has been created. In this work the ground-based remote sensing and GOES satellite data were used to interpolate the original radiosonde measurements to correct for time and space differences between sondes and AIRS overpasses.…”

Error consistency analysis scheme for infrared ultraspectral sounding retrieval error budget estimation

“…state vector or retrievals) (Tobin et al 2006, Pougatchev et al 2009, Larar et al 2010. For example, Tobin et al (2006) used a multi-instrument/platform correlative measurement dataset to build the bestestimated atmospheric state for each individual satellite measurement for validation.…”