Clive Rodgers

Abstract:

The Tropospheric Emission Spectrometer (TES) is a high-resolution spaceborne sensor that is capable of observing tropospheric species. In order to exploit fully TES's potential for tropospheric constituent retrievals, an accurate and fast operational forward model was developed for TES. The forward model is an important component of the TES retrieval model, the Earth Limb and Nadir Operational Retrieval (ELANOR), as it governs the accuracy and speed of the calculations for the retrievals. In order to achieve the necessary accuracy and computational efficiency, TES adopted the strategy of utilizing precalculated absorption coefficients generated by the line-by-line calculations provided by line-by-line radiation transfer modeling. The decision to perform the radiative transfer with the highest monochromatic accuracy attainable, rather than with an accelerated scheme that has the potential to add algorithmic forward model error, has proven to be very successful for TES retrievals. A detailed description of the TES forward model and Jacobians is described. A preliminary TES observation is provided as an example to demonstrate that the TES forward model calculations represent TES observations. Also presented is a validation example, which is part of the extensive forward model validation effort. © 2006 IEEE.

Abstract:

We describe the approach for the estimation of the atmospheric state, e.g., temperature, water, ozone, from calibrated, spectral radiances measured from the Tropospheric Emission Spectrometer (TES) onboard the Aura spacecraft. The methodology is based on the maximum a posteriori estimate, which mathematically requires the minimization of the difference between observed spectral radiances and a nonlinear model of radiative transfer of the atmospheric state subject to the constraint that the estimated state must be consistent with an a priori probability distribution for that state. The minimization techniques employed here are based on the trust-region Levenberg-Marquardt algorithm. An analysis of the errors for this estimate include smoothing, random, spectroscopic, "cross-state," representation, and systematic errors. In addition, several metrics and diagnostics are introduced that assess the resolution, quality, and statistical significance of the retrievals. We illustrate this methodology for the retrieval of atmospheric and surface temperature, water vapor, and ozone over the Gulf of Mexico on November 3, 2004. © 2006 IEEE.

Abstract:

Spectroscopic measurements of BrO using direct sun and zenith-sky viewing geometries are combined in an optimal estimation retrieval algorithm to obtain tropospheric and stratospheric columns of BrO. Seventy-two twilight periods are investigated over Lauder, New Zealand (45.0°S, 169.7°E), between March 2001 and April 2003. A direct comparison between tropospheric and stratospheric columns retrieved at 80°, 84°, and 87° solar zenith angles (SZAs) from the spectroscopic measurements and those calculated by the three-dimensional chemical transport model SLIMCAT shows good agreement. The stratospheric Bry loading of 21 pptv from the SLIMCAT calculations is consistent with the ground-based measurements. The seasonal and diurnal variation of the stratospheric BrO columns evident from the ground-based measurement retrievals is well described by the SLIMCAT model. The tropospheric column retrievals illustrate a high variability with a mean value of 0.2 pptv if the troposphere is assumed to be well mixed. An upper limit of 0.9 pptv is established for the ubiquitous BrO tropospheric column at 80° under cloud free conditions. Copyright 2004 by the American Geophysical Union.