Sea surface temperature estimation by AVHRR spilt window function - A case studies by using Mutsu Bay
Ryuzo Yokoyama, Sumion Tanba
Department of Computer Science
Faculty of Engineering Iwate University
4-3-5 Morioka Iwate Japan 020
Abstract
By using the match-up data sets of the AVHRR brightness temperatures of NOAA-9 and the buoy sea surface temperatures in Mutsu window functions (SWFs) were evaluated The match ups were carefully screened from the HRPT scenes of all seasons in 1985-1988 The temporal and the spatial coincidences are within 30minutes and one pixel resolution respectively The RMSDs were in the range of 0.69~2.31 Most SWFs accompanied with larger RMDs increased their values due to larger biases The statistics of errors delicately depended upon the coefficients of SWFs which were determined by atmospheric profiles or match up data set used in the derivation .for better SST estimation the SWF should be calibrated by a regional match up data of the investigation.
Introduction
The sea surface temperature (SST) imagery remotely sensed by the Advanced Very High Resolution Radiometer (AVHRR) aboard the NOAA satellite series have been conveniently used in various fields e.g oceanography meteorology fishery etc As the thermal radiation from the sea surface is exposed to atmospheric effects many works have been done to investigation its transmittance mechanism A multiple window method (WMWM) as been developed as one of the most promising error correction algorithms (Anding and Kauth (1970 ) Maul and Sidran (1970) Prabhakara et al. (1974) McMillin and Crosby (1975) deshamps and Phulphin (1980) for the temperature detection the AVHRR is equipped with three spectral bands of Ch 3 (3.5~ 3.9
m m) ch.4 (10.5~11.5
m m) and ch.5 (11.5.~12.5
m m) which were selected according to the MWM Nowadays a simplified algorithm were selected according method which uses the ch. 4 and the ch.5 brightness temperatures have been popularly used.
Over those various SWfs have been proposed as known in Table -1 The accuracy of the SWf is evaluated by a root mean square of deviations (RMSD) between the sea truth and the estimated SSt The RMSd of an SWF depends upon both truth and the a match up data set used in the validation rest In most cases their RMSDs were claimed in the range of 0.5~1.2
oC.
As the atmospheric profiles are effected by regional weathers and /or climates an SWF obtained at a region might not be applicable to other regions The quality of the match -up data set are directly related to the error statistics in the results .It is necessary to proceed more comparative studies of SWfs by using various data sets on the base of the seasons the geography and the data quality.
This paper is concerned with a comparative study of the fourteen published SWFs by using the match up data sets of Mutsu Bay This is an extended results of Yokoyam a and Tanba (1988) with increased number of match -ups.
Published split window functions.
A general structure of the SST estimation function
via the ch.4 and the ch.5 brightness temperatures (X
4 and X
5=
respectively) can be
Y = a X4 + b (X4 - X5) + g---------------------(1)
Where Y is the estimated SST the coefficients of
a,
band
g. Depend upon various factors e.g atmospheric effects air sea interacting effects improper sensor calibration contamination in the optical systematic the SST estimation function contamination in the optical is characterized by the value of
a it is theoretically induced to be one from the transmission model of the ch 4 and the ch.5 radiations (Mc.millin) and Crosby) the values can be modified around one by minor adjustments Table 1 shows a list of SWFs published in these a list of SWFs published in these ten years.
