Calculation Of Brightness Temperature Research Articles

Radiative transfer for a three-dimensional raining cloud

Satellite-sensor-based microwave brightness temperatures for a three-dimensional raining cloud over a reflecting surface are computed by using a radiative transfer model based on the discrete-ordinates solution procedure. The three-dimensional model applied to a plane layer is validated by comparison with results from a one-dimensional model that is available in the literature. Results examining the effects of cloud height, rainfall rate, surface reflectance, rainfall footprint area, and satellite viewing position on one- and three-dimensional brightness temperature calculations are reported. The numerical experiments indicate that, under certain conditions, three-dimensional effects are significant in the analysis of satellite-sensor-based rainfall retrieval algorithms. The results point to the need to consider carefully three-dimensional effects as well as surface reflectance effects when interpreting satellitemeasured radiation data.

Mapping of waterlogged and salt-affected soils using microwave radiometers

Abstract Waterlogging and salinity are two major problems identified in coastal regions. No precise remote sensing techniques are available to map the areas affected by these two factors. In order to study the feasibility of using microwave radiometers, numerical calculations of brightness temperature have been carried out over one- and two-layered models representative of waterlogged and salt-affected areas. The behaviour of brightness temperature shows characteristic values over waterlogged and salt-affected areas. The results presented in this paper show the utility of microwave radiometers in mapping waterlogged and salt-affected areas.

Laser photoelectron sources of high apparent brightness

By focusing an ultraviolet laser beam to a small spot on an appropriately shaped cathode, one can obtain photoelectron beams of 106A . cm-1. sr-1brightness. Such a continuous electron source may be useful in electron beam lithography and other applications. Calculations of current densities, brightness, and emitter temperature rises are presented.

Polarized microwave radiation transfer in precipitating cloudy atmospheres: Applications to window frequencies

A microwave radiation transfer model taking into account Mie scattering polarization effects is developed for a plane‐parallel precipitating cloudy atmosphere. In the model the azimuthally averaged Mie scattering phase matrix elements are expressed in terms of double Legendre polynomial expansion and the cloud temperature is approximated by a linear function of the optical depth. The complete solution of the fundamental transfer equation is derived utilizing the discrete‐ordinates method for horizontal and vertical polarization components. Using this model, the brightness temperature and degree of polarization for three microwave window frequencies of 19.35, 37.0, and 85.5 GHz are calculated for a number of rainfall rates over both land and ocean surfaces. We show that the brightness temperature computed for 85.5 GHz using a simple Rayleigh scattering approximation is underestimated by about 7°K for a layer thickness of 4.7 km and a rainfall rate of 5 mm/hr. Effects of the Mie scattering function and nonisothermal cloud structure must both be included for brightness temperature calculations of 37 and 85.5 GHz when thick precipitating clouds are involved. Moreover, we also find that there is a significant degree of polarization for emergent radiation of 19.35 GHz at a zenith angle of 50° under a light rainfall condition over ocean surfaces. Over land surfaces, polarization produced by precipitating clouds is rather small for the three window frequencies. Finally, we show that the existence of ice particles in the upper part of a precipitating cloud largely reduces the upward radiances of the 85.5 GHz frequency.

Thermal radio emission from Jupiter and Saturn

Microwave brightness temperature calculations have been carried out for a number of model atmospheres for Jupiter and Saturn. The models considered are characterized by helium to hydrogen number mixing ratios which range from 0 to 0.2. Gaseous ammonia is assumed to be a trace constituent in all the models. The ammonia abundance below the (NH 3) cloud level is a free parameter which is determined by comparing the observed thermal spectrum of Jupiter and the total spectrum of Saturn with the model calculations. The theoretical microwave spectra corresponding to those models in which the ammonia abundance is that expected from an atmosphere containing a solar abundance of elements are found to be in generally good agreement with the observations. This result is shown to be nearly independent of the helium to hydrogen ratio for the models considered. There is no evidence at this time that a non-thermal component contributes to Saturn's microwave spectrum.