Estudo das variacoes das funcoes-peso em microondas sobre o Brasil, utilizando o modelo ATM / Study of variations of the weighting functions over Brazil, using the ATM model

AUTOR(ES)
DATA DE PUBLICAÇÃO

1999

RESUMO

The weighting functions of the ten Advanced Microwave Sounding Unit (AMSU) channels of Advanced TIROS-N/NOAA Operational Vertical Sounder (ATOVS), calculated from the Atmosphere Transmission at Millimetric and Submillimetric Wavelengths (ATM) model, were compared with those from the AMSU/ATOVS. Among the ten channels, five refer to the oxygen absorption lines around 57,29 GHz, that constitute the AMSU-A (channels 2, 4, 5, 6 and 8), while the other five are associated to water vapor absorption lines around 183,31 GHz, that compose the AMSU-B (channels 16, 17, 18, 19 and 20). Standard atmospheric vertical profiles (tropical and midlatitudes in summer and winter) implicit in the ATM model and the temperature and humidity climatological vertical profiles of regions in Brazil were utilized. The current version of the ATM model calculates the absorption coefficient of the atmospheric gases in microwave spectrum utilizing atmospheric vertical profiles of pressure, temperature, humidity and concentration of gases. Some input parameters are also included, such as surface emissivity, sensor view angle and central frequency of the channel. The weighting functions calculated from the standard atmospheric vertical profiles of the model were compared with those from the AMSU and Brazil. Moreover, spacial and seasonal variations of the weighting functions over Brazil were studied; the influence of the surface emissivity and of the sensor view angle in the calculation of weighting functions was verified. The results show consistency among the weighting functions for the majority of the AMSU-A channels. For the AMSU-B channels, a discrepancy among the weighting functions obtained with the climatological profiles was observed. This suggests a more specific definition of the weighting functions for Brazil. The surface emissivity and the sensor view angle exerted strong influence on some of the weighting functions of AMSU-A and AMSU-B channels.

ASSUNTO(S)

atenuacao atmosferica modelo de transferencia radiativa funcao peso espectro das microondas sondagem atmosferica espectropia da absorcao meteorologia por satelite modelo atm

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