NOAA卫星资料.doc
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1、.-(JPL Publication D-14070)NOAA/NASA AVHRR Oceans PathfinderSea Surface Temperature Data SetUsers Reference ManualVersion 4.0April 10, 1998Jorge Vazquez (JPL/Caltech)Kelly Perry (JPL/Caltech)Kay Kilpatrick (RSMAS/University of Miami)Appendices were provided by:Katherine Kidwell (NOAA), Robert Evans
2、(University of Miami), Guillermo Podesta (University of Miami), Kay Kilpatrick (University of Miami) Updated 16 Dec 2002, Ed Armstrong, JPL PO.DAAC 1.0 INTRODUCTION2.0 ALGORITHMS ANDDATAPROCESSING- 2.1 Algorithm Overview- 2.2 Accuracy of AVHRR-derived SSTs- 2.3 Processing Flow3.0 DATASETDETAILS (Equ
3、al-Angle Products)- 3.1 Overview- 3.2 Equal Angle Best SSTData- 3.4 Equal Angle All SST- 3.5 Matchup Database- 3.6 Equal Area4.0 DATAINFORMATIONANDACCESS- 4.1 Regional Subsetting and Extraction Using WWW- 4.2 Downloading the Data Using Anonymous FTP- 4.3 Information About Processing Status5.0 READIN
4、G AND USING DATASETS- 5.1 Conversion of DN to SSTs and Pixel Coordinate to Latitude and Longitude- 5.2 Read Software- 5.3 Attributes6.0 REFERENCES7.0 ACKNOWLEDGMENTSAPPENDIX A- Satellite and InstrumentAPPENDIX B - Coefficients and ValidationAPPENDIXC - Quality Flags Assignments and InformationAPPEND
5、IXD - Read SoftwareAPPENDIX E - Science Working Group and JPLTeamAPPENDIX F - AcronymsAPPENDIX G - AVHRRPathfinder Oceans SSTAlgorithm1.0 INTRODUCTIONThis document describes the NOAA/NASA AVHRR Ocean Pathfinder Sea Surface Temperature (SST) products, their production, quality assurance, archive, and
6、 methods of data acquisition. It briefly discusses the Advanced Very-High Resolution Radiometer (AVHRR) instrument from which the data are derived, and the National Oceanic and Atmospheric Administration (NOAA) satellite platforms. Pathfinder SST data are accessed through the Earth Observing System
7、Data and Information System (EOSDIS) Physical Oceanography Distributed Active Archive Center (PO.DAAC) at the Jet Propulsion Laboratory (JPL). The document is specifically intended to cover the version 4.1 and version 4.0 data sets. A brief description of earlier algorithm versions 1.0 and 3.0 may b
8、e found in the Appendix B. The document is organized with section 2 containing a brief history of the processing of SST from the AVHRR Instrument, section 3 gives an overview of the different products available based on spatial and temporal resolutions, section 4 is a summary of how to access the da
9、ta and relevant documentation and appendices A-G discuss more detailed information on algorithm development, quality flag assignment, and validation. 2.0 ALGORITHMS ANDDATA PROCESSING2.1 Algorithm OverviewCurrent retrieval algorithms for sea surface temperature from AVHRR are based largely upon the
10、multi-channel sea surface temperature (MCSST) algorithm (McClain et al., 1985) which may be written as:SST=1 + 2T4 + (T4 - T5)(1)where 1 and 2 are constants determined through a least-squares fit to in-situ data, T4, T5, are brightness temperatures as derived from channels 4 and 5 (see table 1) and
11、is a weighting factor based on the knowledge of known absorption coefficients (Emery et al., 1994). In this form the linear model has no correction for water vapor attenuation. A nonlinear SST algorithm (NLSST) was introduced that incorporates an initial estimate of the SST field, where the coeffici
12、ents are calculated for different water vapor regimes as defined by (T4 - T5) differences. The form of the NLSST algorithm used to derive the Pathfinder SST becomes:SST=1 + 2T4 + 3 (T4 - T5)*Tsurf + 4 (sec()-1)(T4 - T5)(2)where the s are still coefficients based on a least squares fit to in-situ dat
13、a and T4, T5 are the brightness temperatures in channels 4 and 5. Theta is the satellite scan angle or the incidence angle of the incoming radiation based on the horizontal plane of the satellite, and Tsurf is a first guess sea surface temperature field; in this case the Reynolds optimally interpola
14、ted (OI) sea surface temperature data. A non-linearity in the algorithm arises because of the Tsurf term and the 4 coefficients being calculated over two different (T4 - T5) differences. In version 4.0 and 4.1 of the algorithm the coefficients are calculated for T4 - T5 0.7. This form of the algorit
15、hm was approved for the reprocessing of the MCSST data by the AVHRR Oceans Science Working group because it tended to lower the overall bias over the widest possible environmental conditions (Evans and Podesta., 1996). A nonlinearity arises from the coefficients being calculated over different water
16、 vapor regimes corresponding to (T4 - T5); the V1 algorithm calibration coefficients were calculated yearly for three different water vapor regimes or T4-T5 channel differences. All the algorithms used the non-linear SST algorithm (NLSST), developed and used operationally by NOAA/NESDIS. Earlier for
17、ms of the algorithm such as Version 3.0 also use the nonlinear SST algorithm (equation 2) with calibration coefficients calculated for two different water vapor regimes or T4-T5 channel radiance differences and over 5 month periods centered on each month. The improvement of the version 4.1 data set
18、over previous algorithms such as version 1.0, 3.0 and 4.0 lies in the use of a tree algorithm to calculate the quality flags, thus making the procedure of quality flag assignment more objective. The tree algorithm leads to a quality flag between 0-7 being assigned to a pixel value, with 0 being the
19、lowest quality and 7 being the highest quality. For version 4.1 pixels defined as best are assigned a quality flag greater than or equal to 4. In earlier versions pixels flagged as best were assigned a quality flag of 3. For more details see http:/www.rsmas.miami.edu/groups/rrsl/pathfinder/Processin
20、g/proc_index.html (Evans and Podesta, 1998) or appendix G. Appendix C contains details on the tests used to assign the quality flags for version 4.1. The information is provided by Guillermo Podesta and Katherine Kilpatrick at the University of Miami. The currently available Version 4.1 Pathfinder d
21、ata sets cover 1985-1999. Version 4.1 interim data is available from 2000-2003. For updates on the status of the Pathfinder SST time series please see the PODAAC AVHRR Pathfinder homepage http:/podaac.jpl.nasa.gov/sst/. 2.2 Accuracy of AVHRR-derived SSTsWork is currently underway to determine the ac
22、curacy of the data (see Vazquez et al., 1998 or Evans et al., 1996). Current results indicate that the accuracy is regionally dependent and influenced by the water vapor content in the atmosphere. However more work needs to be done to confirm this. Some points of interest from work with previously a
23、vailable AVHRR derived SSTs include:1)The SST measurement is of the skin temperature, and not the bulk temperature (Schluessel et al., 1990).2)Atmospheric water vapor partly affects the retrieval, but no independent water vapor data sets are used in the algorithm (Emery et al, 1994).3)Most successfu
24、l uses of past MCSST data concentrated on identifying spatial temperature gradients (Gulf Stream fronts, etc.) rather than absolute temperature values. The present calibrations are designed to provide consistency over the duration of the 5-channel data record.4)Cloud masking in any all-pixel image c
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