XDS: TOMS

Global data derived from the Total Ozone Mapping Spectrometer (TOMS) instrument on the Earth Probe satellite, consisting of daily values of aerosol index, ozone, and reflectivity remapped into a regular 1×1.25 deg grid. Users of these data should acknowledge the support of the NASA Goddard Ozone Processing Team.

Daily values of ozone, aerosol index, and reflectivity at each grid cell are taken from three ascii files and combined into one monthly netCDF file.

Ozone
Ozone measurements are given in Dobson units and are integers with 3 significant figures. A Dobson Unit represents the physical thickness of the ozone layer if it were brought to the Earth’s surface. A value of 300 Dobson units equals three millimeters or 1/10th of an inch. Missing values denote flagged data, i.e., data that could not be collected due to lack of sunlight or other problems.

Aerosol Index
The data are an aerosol index formed directly from the measured radiances in two TOMS channels. Positive values generally represent absorbing aerosols (dust and smoke) while negative values represent nonabsorbing aerosols. The identification is not perfect because of geophysical reasons (e.g., aerosol too low to the ground).

Reflectivity
The solar irradiance reflected up to a spacecraft from the surface of the Earth can be used to calculate reflectivity. Reflectivity calculated for specific bandwidths is needed for the calculation of total column ozone from TOMS instrument. Reflected radiation can come from two surfaces, the ground, and the tops of clouds. Reflectivity is determined from the measurements at 380 nm, or 360 nm in the case of Earth Probe. Clouds are clearly defined and recognizable in images produced using TOMS reflectivity data. Data are in percent.

Data are available from July 25, 1996 – December 31, 2005.
This datastream is replaced by gecomiX1.a1. See the Ozone Monitoring Instrument documentation

Data for each day are gridded into 1-degree latitude zones by 1.25-degree longitude zones. Latitudes go from -90 degrees (the south pole) to 0 degrees (the equator) to +90 degrees (the north pole) in 1 degree steps, so there are 180 latitude zones. The first zone extends from -90 to -89, so the grid cell is considered to be centered on -89.5. Similarly, longitudes go from -180 (west longitude) to 0 (Greenwich, England) to +180 (east longitude) in 1.25 degree steps, so there are 288 longitude zones (360/1.25). The first longitude zone extends from -180 to -178.75, so the grid cell is considered to be centered on -179.375.

gectomsaerosolindexX1.00
gectomsozoneX1.00
gectomsreflX1.00

TOMS Website

Vasile Tudor Garbulet

ARM Data Center

Institution
TOMS Website

Reprocessing Date
2014100:
gectomsX1.a1 from 19960722-20051231 were reprocessed via the input data based on the new version 8 algorithm.

Start End Reprocessing

Reason Reprocessing

The following note is from the TOMS Web site. “November 2000 Special Note: After four years in orbit, the Earth Probe TOMS instrument is experiencing some wavelength-dependent calibration drift which is affecting the aerosol index calculation (whereas the effect on total ozone calculation is very small). The problem is being looked into which could lead to a re-computation of recent aerosol index values and re-generation of recent aerosol index images for Earth Probe TOMS.”

Check the Data Quality Reports for these data via the ARM DQR web service DQR040920.2 discusses the changes to version 8 of the TOMS algorithm and questions whether data prior to September 2004 should be replaced with data based on the new algorithm.

Beginning September 2004, the data are based on the version 8 TOMS algorithm. See Version 8 Algorithm Theoretical Basis Document.

GEC    Global Earth Coverage
TOMS   Total Ozone Mapping Spectrometer

Torres, O, PK Bhartia, JR Herman, A Sinyuk, P Ginoux, and B Holben. 2002. “A Long-Term Record of Aerosol Optical Depth from TOMS Observations and Comparison to AERNOET Measurements.” Journal of the Atmopsheric Sciences 59(3): 398-413, doi: 10.1175/1520-0469(2002)059<0398:altroa>2.0.co;2

Torres, O, PK Bhartia, JR Herman, Z Ahmad, and J Gleason. 1998. “Derivation of aerosol properties from satellite measurements of backscattered ultraviolet radiation: Theoretical basis.” Journal of Geophysical Research: Atmospheres 103(D14): 17,099-17,110, doi: 10.1029/98jd00900