Linear retrieval, validation and mapping of the sea surface temperature over western mid-latitude North Pacific using Seasat SMMR data

Abstract

The Scanning Multichannel Microwave Radiometer (SMMR) aboard the Seasat satellite measured emitted radiation in both horizontal and vertical polarizations at microwave frequencies of 6.6, 1069, 18.0, 21.0 and 37.0 GHz. Retrieval algorithms, for sea surface temperature (SST) determination, from subsets of one to three SMMR channels, are obtained by a two-step statistical technique. The technique first selects the best subsets of a given size defined by an R2 criterion (coefficient of determination), of a given size by the application of an efficient leaps and bounds technique on a statistical data base. It then performs a regression analysis on the selected subsets. The statistical data base employed a large (600) set of seasonally and geographically diverse atmospheric and surface parameters for radiative transfer calculations. The results of the study of one to three-channel subset retrieval algorithms indicate the possibility of using 6.6 V, 6.6 H and 18 V channels for SST determinatidn from Seasat-SMMR data. A comparison of SMMR-SST derived from three channels mentioned above and expendable bathythermograph (XBT) measurements over the North Pacific provided an r.m.s. difference of 1.4 K which is comparable to the accuracy obtained from a five-channel subset (6 6 V, 6-6 H, 10-69 H, 180V, 21 OH) retrieval algorithm. The retrieval technique has the ability to recognize severe noise in brightness temperature measurements which may lead to unacceptable parameter retrieval. This may be achieved by setting up a quality control criteria either using different subsets of the same size or of different sizes. The three-channel retrieval compares within 1.2 K with Chester's algorithm, which is being used at the Jet Propulsion Laboratory for geophysical processing. Ten-day and monthly average SMMR-SST contour maps are produced using three-channel retrieval for the period 7 July-6 August 1978 over the western North Pacific, 20°-50° N, 140°-180° E. These contour maps are compared against similar maps obtained from Chester's algorithm and ship's observations. All the SMMR-SST maps show the major climatological features and are in reasonable agreement with ship's SST maps.