A method of determining ocean–atmosphere latent heat flux using the Special Sensor Microwave/Imager (SSM/I) and the Advanced Very High Resolution Radiometer (AVHRR) is presented and evaluated. While sea surface temperatures are retrieved from AVHRR data with an accuracy of 0.5–1.0 K, the near-surface wind speed and the surface air humidity are retrieved from measurements of the SSM/I with accuracies of 1.4 m s−1 and 1.1 g kg−1, respectively. The latent heat flux is then computed with a stability-dependent bulk parameterization model. The derived fluxes are compared to globally distributed instantaneous shipboard and buoy measurements and to monthly averages of 2° × 2° longitude and latitude bins. The standard error for instantaneous flux estimates is approximately 30 W m−2, and that for monthly averages decreases to 15 W m−2. Additionally, a 1-yr time series of latent heat flux at the weathership M in the North Atlantic and two shorter time series during the Tropical Ocean Global Atmosphere Coupl...

https://journals.ametsoc.org/doi/pdf/10.1175/1520-0442(1997)010%3C2782%3AEOSDLH%3E2.0.CO%3B2

Evaluation of Satellite-Derived Latent Heat Fluxes

In this paper an algorithm for retrieving precipitation from Special Sensor Microwave/Imager (SSM/I) satellite microwave data is presented for rainfall occurring over both ocean and land. This algorithm is basically derived from the results of a microwave radiative transfer model of plane-parallel rain clouds and combines the emission and scattering regimes. The features of the algorithm are as follows: (1) a linear function of horizontally polarized brightness temperature at both 19.35 and 85.5 GHz is used as a parameter to relate rainfall rate, which shows no saturation for rainfall rates up to 50 mm/h; (2) the relationship between the linear function and the rainfall rate is closer to linearity than the relationship between brightness temperature of a single channel and rainfall rate, and therefore the beam-filling problem is less serious than for single-channel algorithms; (3) the algorithm includes a correction to a beam-filing problem that was made on the basis of observational evidence; (4) the threshold for precipitation is derived from the SSM/I data themselves, which includes climatological information; and (5) the algorithm is less sensitive to freezing level height and surface temperature than emission-based algorithms. Validation of the algorithm is made using surface radar and rain gauge data. The validation shows that rainfall retrievals over ocean are in a satisfactory agreement with the surface observations. Over land, heavy rainfall rate can be detected although the disagreement is significant.

Retrieval of precipitation from satellite microwave measurement using both emission and scattering

The Special Sensor Microwave/Imager (SSM/I) flying as part of the U.S. Defense Meteorological Satellite Program measures millimeter-wave radiation emerging from the Earth-atmosphere system at different directions of polarization that can be used to measure oceanic surface wind speed. The radiative transport within the radiometer channels is studied theoretically for a large set of oceanic/atmospheric situations with respect to surface wind speed variations. Statistical retrieval coefficients for the recoverage of surface wind speeds from the satellite measurements are then derived via regression analysis of the synthetic measurements simulated. The theoretically estimated accuracy for the globally valid passive wind speed retrieval is 1.4 m/s under conditions where no heavy rain hampers the surface-leaving radiation in reaching the satellite. The technique is validated with in situ wind fields over the North Sea being objectively analyzed from routine wind and pressure observations.

Surface wind speeds over the North Sea from special sensor microwave/imager observations

The feasibility of using spaceborne microwave radiometry to retrieve geophysical parameters is described. The study concentrates on the development of inversion techniques for multichannel spaceborne radiometers, especially the statistical inversion approach. The applications of the planned MIMR (Multi-Frequency Imaging Microwave Radiometer) instrument are discussed. The inversion algorithms used are conventional algorithms for different applications and the statistical inversion approach. Comparisons between results from different inversion algorithms are presented. The statistical inversion approach has been found to give promising parameter retrieval accuracies and has the potential to improve the operational use of passive spaceborne remote sensing. An analysis of the sensitivity of the radiometer apparent temperature to different geophysical parameters and the statistical behavior of the atmospheric transmissivity are presented. >

Development of geophysical retrieval algorithms for the MIMR

Advances in passive remote sensing of the ocean

Sea-surface temperature retrievals have been tested on 2 months of Nimbus-7 scanning multichannel microwave radiometer data. Using the prelaunch versions of the instrument calibration and geophysical parameter retrieval algorithms the initial results were poor. Improved algorithms produced substantially better results. It appears that at least for the night-Southern Hemisphere portion of the Nimbus-7 orbit, a rms measurement accuracy of 1.45°C has been achieved. Similar tests with wind speed retrievals yield an accuracy of 2.7 m/s rms with no substantial differences between day and night measurements but limited by availability of surface observations to the Northern Hemisphere. Moreover, it appears that the retrieved wind speed is more nearly related to the square of the wind observed at the surface than to the wind itself.

Daesoo Han

Papers

Retrieval of Ocean Surface Parameters from the Scanning Multifrequency Microwave Radiometer(SMMR) on the Nimbus-7 Satellite