Search Results

You are looking at 1 - 3 of 3 items for :

  • Author or Editor: Henry E. Fleming x
  • Journal of Applied Meteorology and Climatology x
  • Refine by Access: All Content x
Clear All Modify Search
Henry E. Fleming

Abstract

Computed tomography is a medical diagnostic technique in which x-ray transmission measurements at numerous angles through the human body are processed by computer to produce cross-sectional pictures of the body. A modification of this technique, using emitted infrared or microwave radiation instead of transmitted x-ray radiation, can be applied to satellite radiance measurements taken along the orbital track at various angles. Cross sections of the vertical atmospheric temperature structure (or the gaseous constituent density structure) are retrieved from the collection of radiance measurements taken at various angles and frequencies. The advantage of this technique over conventional remote sensing methods is the additional information acquired by viewing a given point in the atmosphere at several angles as well as at several frequencies. The physical and geometric concepts involved are discussed along with the mathematical formulation of the problem and the practical aspects of applying the technique. A method of solution of the resulting large, sparse system of equations is given and is applied to simulated case studies. Temperatures retrieved by the computed tomography technique, when compared with those retrieved by conventional methods, showed an overall average improvement in accuracy of as much as 34% in the study.

Full access
Henry E. Fleming
,
David S. Crosby
, and
Mitchell D. Goldberg

Abstract

Layer-mean virtual temperatures retrieved from satellite measurements are more accurate than retrievals at specific pressure not only because an averaging process is involved, but also because of advantages in the retrieval process. In this note, a “retrieval efficiency” is derived to express this advantage over simple averaging as a function of layer thickness. The efficiency is examined for two common cases of retrieval initial guess: a statistical sample mean and a forecast profile obtained from a numerical prediction model. The advantage of the layer-mean retrieval clearly is demonstrated in both cases.

Full access
Henry E. Fleming
,
David S. Crosby
, and
Arthur C. Neuendorffer

Abstract

It is generally assumed that atmospheric transmittance functions are known to an accuracy of no better than about five to ten percent. Consequently, one can expect a major impact of these errors on temperature retrieves based on the inversion of the radiative transfer equation, as opposed to regression methods that do not explicitly use transmittance functions. A numerical simulation study of the sensitivity of the retrieved temperature profiles to errors in transmittance is described. The study shows that most of the transmittance error is propagated into the retrieved profiles in the form of a bias error. A technique for removing this large bias component of the error is given. Furthermore, it is shown how the improper use of regularization transforms sonic of the bias error into an unremovable component of random error. Finally, we show results that indicate how well the bias-error removal technique works in practice using real data. It is found that, despite errors of measurement and errors in the transmittance functions, one can retrieve temperature profiles of good quality.

Full access