Temporal Variations of Land Surface Microwave Emissivities over the ARM Southern Great Plains Site
نویسندگان
چکیده
Land surface microwave emissivities are important geophysical parameters for atmospheric, hydrological, and biospheric studies. This study estimates land surface microwave emissivity using an atmospheric microwave radiative transfer model and a combination of the Special Sensor Microwave/Imager (SSM/I) satellite observations and data from the Atmospheric Radiation Measurement (ARM) Program Southern Great Plains (SGP) site during October 1995. Emissivities are retrieved for both clear and cloudy conditions. Emissivity standard deviations of ~0.035 were found at the SGP site. Much of the variability is produced by a distinct diurnal cycle. The emissivity variability at each SSM/I overpass time (0630, 1100, 1730, and 1000 local time) is about half that for all four times combined. Early morning emissivities are ~0.06 less than those at other times, while the polarization differences at the four times are similar. This behavior is likely the result of dew and surface rewetting effects. Ground observations of dewpoint and temperature difference between air and skin support this theory. The surface emissivities have a significant negative correlation with soil moisture which can explain about 60-80% emissivity variance when pentad running means are used. Strong correlations among all 7 SSM/I channels indicate that the emissivities only need to be determined directly for two or three channels.
منابع مشابه
New Technique for Retrieving Liquid Water Path over Land using Satellite Microwave Observations
We present a new methodology for retrieving liquid water path over land using satellite microwave observations. As input, the technique exploits the Advanced Microwave Scanning Radiometer for earth observing plan (EOS) (AMSR-E) polarization-difference signals at 37 and 89 GHz. Regression analysis performed on model simulations indicates that over variable atmospheric and surface conditions the ...
متن کاملEffect of Stratus on Solar Radiation: A Study Using Millimeter Wave Cloud Radar and Microwave Radiometer Data From the Southern Great Plains
Clouds are important players in the global radiation budget with low-level water clouds being one of the most influential types. Classified as stratocumulus and stratus, these water clouds cover 34% of oceans and 18% of land at any given time (Considine et al. 1997). A 50% plus global coverage, a high albedo when compared to the ocean, and temperatures comparable to the surface causes the low s...
متن کاملAMSU-B Observations of Mixed-Phase Clouds over Land
Measurements from passive microwave satellite instruments such as the Advanced Microwave Sounding Unit B (AMSU-B) are sensitive to both liquid and ice cloud particles. Radiative transfer modeling is exploited to simulate the response of the AMSU-B instrument to mixed-phase clouds over land. The plane-parallel radiative transfer model employed for the study accounts for scattering and absorption...
متن کاملFrequency and angular variations of land surface microwave emissivities: can we estimate SSM/T and AMSU emissivities from SSM/I emissivities?
To retrieve temperature and humidity profiles from special sensor microwave/temperature (SSM/T) and advanced microwave sounding units (AMSU), it is important to quantify the contribution of the Earth surface emission. So far, no global estimates of the land surface emissivities are available at SSM/T and AMSU frequencies and scanning conditions. The land surface emissivities have been previousl...
متن کاملRetrieval of Surface and Atmospheric Geophysical Variables over Snow-Covered Land from Combined Microwave and Infrared Satellite Observations
Surface temperature and emissivities, as well as atmospheric water vapor and cloud liquid water, have been calculated from Special Sensor Microwave Imager observations for snow-covered land areas using a neural network inversion scheme that includes first-guess information. A learning database to train the neural network is derived from a global collection of coincident surface and atmospheric ...
متن کامل