Contents of Overpass Data Files The overpass data files contain the data derived from the best-matched TOMS field-of-view (FOV) to a site for every day the TOMS instrument was operational. Each overpass file contains four (4) header records, followed by all the data records. ------------------------------------------------------------------------ Header The file header consists of four (4) records: 1. Site name, ID, and location. 2. Overpass program run information 3. Column headings 4. Marker record. An example of the first header record is: Edmonton/Stony Plain, Canada ID: 21 Lat: 53.55 Lon: -114.10 Alt: 766 In this example, the site ID number is 21, the latitude is 53.55oN and longitude is 114.10oE, and the verified elevation is 766 m.a.s.l. The following FORTRAN code will read the first header: CHARACTER*28 site_name INTEGER*4 site_id, site_alt REAL*4 site_lat, site_lon . . . READ(lun,2) site_name, site_id, site_lat, site_lon, site_alt 2 FORMAT(A30,4X,I3,7X,F7.2,7X,F7.2,7X,I4) . . . An example of the second header record is: Meteor-3 TOMS V.8 Overpass - Generated: 050328 This indicates the spacecraft instrument, the data version used to generate the overpass data, and the date on which the file was generated (created or updated) in YYMMDD format. The third header record contains the column headings for the data records. The header looks like this: MJD Year Day sec-UT SCN LAT LON DIS PT SZA OZONE REF A.I. SOI The contents of each column is described below in the section on Data Records. The fourth header record simply contains a pound-sign (#) in the first column, and signals that the data begin with the next record in the file. ------------------------------------------------------------------------ Data Records Each data record contains fourteen (14) values. They are as follows. MJD Modified Julian Day. Astronomical Julian Day number*, less 2,400,000.5 The number is given to the nearest 1/10 day. Year The four-digit Gregorian year number of the TOMS measurement. Day The day number (day 1 through 366) of the TOMS measurement. sec-UT The number of seconds from midnight, Universal Time. on the day specified by Year and Day. SCN TOMS instrument scan position (1--35 for N7 and EP; 1--37 for Adeos) LAT Latitude of the center of the IFOV. LON Longitude of the same. DIS Distance from site and IFOV center position, in km. PT Terrain pressure at IFOV center, in (atm x 100) SZA Solar zenith angle, in degrees, at time and location of IFOV OZONE TOMS Version-7 best total ozone, in Dobson Units (DU) REF TOMS Version-7 reflectivity at 380 nm (N7, M3) or 360 nm (EP, Adeos). A.I. TOMS Version-7 aerosol index. SOI TOMS Version-7 Sulfur dioxide index. (*) The astronomical Julian day number (JD) is the number of Greenwich mean noons that have occurred since Greenwich noon on 1 January 4713 B.C.E., on the Julian proleptic calendar. This provides an unambigous time index. The Modified Julian Date (MJD) is defined as MJD = JD - 2,400,000.5 . Using the MJD saves having to store the leading two digits, which, for the purpose of this data set are always `24', and makes integral values of MJD begin at Greenwich mean midnight. Additional information about these may be found in the Explanatory Supplement to the Astronomical Almanac. A FORTRAN (or IDL) format specification that would be appropriate for reading a data record is: (F7.1, 1X, I4, 1X, I3, 1X, I5, 2X, I2, 1X, F6.2, 1X, F7.2, 1X, I3, 1X, I3, 1X, F5.2, 1X, F5.1, 1X, F5.1, 1X, F6.2, 1X, I4) ------------------------------------------------------------- South Pole Site (Amundsen-Scott, Ant.; Site No. 111) The overpass algorithm has a minor glitch, which appears to affect only this site. The data are correct, but the TOMS Field-of-View selection algorithm might not be selecting the best FOV. The data in these files (all four spacecraft) should be considered to be provisional for the time being. We hope to have this problem fixed very shortly. ------------------------------------------------------------- Nimbus-7, Meteor-3, and Adeos-1 Data Sets These overpass data sets are complete for the entire operational periods of these instruments. ------------------------------------------------------------- Update Frequency As of the present time, we are not updating the Earth-Probe TOMS overpass data past December 31, 2005. ------------------------------------------------------------- Special-Purpose Overpass Data Sets We currently do not produce special-order overpass data sets, except in connection with collaborative research in which we are directly involved. -------------------------------------------------------------