SAGE III File Format

  1. Level 1B Solar Transmission Product
  2. Level 2 Solar Species Product
  3. Level 2 Cloud Product (from solar data)
  4. Level 2 Lunar Species Product
  5. File Naming Convention
  6. Dataset location

1 - Level 1B Solar Transmission Product

The Level 1B Transmission product contains the SAGE III atmospheric slant path transmission profiles at 85 spectral channels. The profiles are skewed vertically and extend from sea level to an altitude of 100 km in 0.5 km intervals. These data have been geolocated and normalized against exoatmospheric solar measurements to produce slant path transmission profiles. The Level 1B product is only available for solar measurements.

2 - Level 2 Solar Species Product

The Level 2 Solar Species products are produced from the Level 1B Transmission profiles. The content of the Level 2 Solar Species organized by species, each including information on its relative uncertainty. Species are reported in profiles on a geometric altitude coordinate system with a vertical resolution of 0.5 km.

Aerosol Profiles of aerosol extinction are provided at 9 different wavelengths (385, 448, 521, 596, 676, 754, 868, 1019, and ~1550 nm) from the surface or opaque cloud top to an altitude of 40 km, where the contribution due to aerosols becomes negligible at all wavelengths.

In addition, two aerosol products are provided in this list: (1) Stratospheric aerosol optical depth and (2) the ratio of aerosol extinction to the contribution due to molecular scattering at a wavelength of 1019 nm.

Water Vapor Profiles of water vapor are provided in units of concentration from the surface to an altitude of 50 km. A temperature profile retrieved from SAGE III measurements or from a gridded analysis will facilitate computation of relative humidity. The water vapor products are retrieved using a nonlinear least squares approach from the solar occultation measurements of slant path absorption.

Nitrogen Dioxide Profiles of nitrogen dioxide are provided in units of concentration from the tropopause to an altitude of 50 km.

Ozone Three different profiles of ozone are provided in units of concentration over the altitude range 6 to 85 km. One profile is based upon measurements made at short wavelengths in the Hartley-Huggins band and a second profile is based upon measurements made at visible wavelengths in the Chappius band. The third product consists of a composite profile constructed of data from the Chappius band at lower altitudes (below about 55 km) and from the Hartley-Huggins band at higher altitudes (above approximately 55 km). For each of the 3 different ozone products, slant path column density profiles are also included.

Temperature and Pressure The retrieved profiles of temperature and pressure are new products provided by the SAGE III mission. Besides providing a valuable scientific measurement, this data will permit a self-consistent determination of molecular scattering along the limb view which is needed for accurate retrievals of ozone and other species.

3 - Level 2 Cloud Product (from solar data)

The SAGE III instrument detects subvisible and opaque clouds by using measurements of aerosol extinction and their uncertainties at wavelengths of 525, 1020, and 1550 nm. The basic product consists of 3 vertical profiles extending from 0 to 30 km that contain information on the presence of clouds at 0.5 km intervals. Unlike all other Level 2 products, a granule of this product contains a collection of cloud data for one calendar month.

4 - Level 2 Lunar Species Product

The retrieval of constituent profiles from irradiance measurements acquired during lunar occultation events is a new capability for the SAGE III experiment. These retrievals are more complex than those employed for solar events because they account for the spatial and spectral non-uniformity of the surface albedo of the moon and the much lower measurement signal. One important difference between the solar and lunar retrieval techniques is the absence of a Level 1B slant path transmission profile product for lunar occultation retrievals. This is a consequence of not being able to determine limbdarkening curves with sufficient accuracy to calibrate each SAGE III lunar occultation event.

A single scan vertical resolution of the lunar Level 2 products is 1 km. The chemical species concentration data from multiple scans are bin-averaged and reported on a geometric coordinate system with a vertical resolution of 0.5 km to maintain grid spacing compatibility with the solar Level 2 products.

Chlorine Dioxide Profiles of chlorine dioxide are provided in units of concentration for an altitude range of 15 - 25 km.

Nitrogen Dioxide Profiles of nitrogen dioxide are provided in units of concentration from 20 to 50 km.

Nitrogen Trioxide Profiles of nitrogen trioxide are provided in units of concentration for the altitude range of 20 - 55 km.

Ozone Profiles of ozone based upon measurements made at visible wavelengths in the Chappius band are provided in units of concentration from 16 to 35 km.

5 - File Naming Convention

Following is a list of products and the file naming convention for each product that shall be generated by SAGE III SCF processing:

Product Filename Format
L1B Solar Transmission Binary Products g3a.tb.{xxxxxxXXvzz.zz}
L1B Solar Transmission HDF Products g3a.t.{xxxxxxXXvzz.zz}{xxxxxxXXvzz.zz}
Level 2 Solar Binary Products g3a.sspb.{xxxxxxXXvzz.zz}
Level 2 Solar HDF Products g3a.ssp.{xxxxxxXXvzz.zz}
Level 2 Lunar Binary Products g3a.lspb.{xxxxxxXXvzz.zz}
Level 2 Lunar HDF Products g3a.lsp.{xxxxxxXXvzz.zz}
Level 2 Cloud Binary Products g3a.cldb.{xxxxxxXXvzz.zz}
Level 2 Cloud HDF Products g3a.cld.{xxxxxxXXvzz.zz}


Tag Description
t Level 1B transmission profiles
ssp Level 2 Solar species profiles
lsp Level 2 Lunar species profiles
cld Level 2 Cloud product
{xxxxxxXX} Event ID (6 digit orbit number, 2 digit event type)
{vzz.zz} Software version number

6 - Dataset location

The SAGE III data are mirrored from NASA Langley DAAC in a predefined directory structure as follows:

[shortname.versionid] / [acquisitiondate], where:
[shortname.versionid] is the collection identifier. (e.g., g3alsp.002).
[acquisitiondate] is the date the measurement was taken. (e.g., 2002.06.22).

Data files in HDF-EOS format are stored in the appropriate directory based on collection and acquisition date. Corresponding metadata files in Extensible Markup Language (XML) format are also stored in the appropriate directory.

NOTE: The SAGE III data was downloadded from the EOS Data Gateway, Langley DAAC Data Pool and it should be noted that the version number on that system represents the Earth Science Data Type version rather than the SAGE III Data version. Accordingly, the newly-released V3 data is stored as version '002'.