MOPITT Algorithm Theoretical Basis Document (ATBD) (Level 1 to Level 2)

Retrieval of Carbon Monoxide (CO) Profiles and Column Amounts of CO and Methane (CH4) from MOPITT Observed Radiances

Abstract:

This document briefly outlines the Measurement of Pollutants in the 
Troposphere (MOPITT) investigation and describes the physics and mathematics
of the algorithms that invert the radiances measured by the MOPITT instrument,
to produce the geophysical data products resulting from this investigation.

These products are:
  1.  Total column amounts of carbon monoxide (CO) and methane (CH4), and
  2.  Vertical profiles of CO.

The Level-2 data products are described elsewhere.

The algorithms described in this version of the ATBD are scientific or
prototype algorithms.  These are being developed on the NCAR EOS Science
Computing Facility (SCF), where they will be used to explore different
approaches to the most efficient recovery of the information from the MOPITT
radiances, while taking account of the instrument effects (e.g. noise,
instrument balance condition, etc.) expected to be present in the flight 
data. Subsequently, these algorithms will be incorporated in formally 
documented software which will be developed and tested on the SCF. This 
software will then be installed at the Langley DAAC, where their 
operation and outputs will be verified prior to launch.  They will be 
applied to data acquired in orbit during the flight phase of the program.

This first version of ATBD reflects the present status of the 
prototype algorithms, which are undergoing rapid development. With 
time, the algorithms will evolve to include the capability to handle 
more complex situations, and the ATBD will be updated to reflect 
these increased capabilities.  

The steps in that evolution are planned as follows:

1. CO profile retrieval algorithm for nighttime (without the
   knowledge of total column amount), clear sky and known surface 
   emissivity,  assuming CO is the only constituent in the atmosphere;

2. CO profile retrieval algorithm for daytime under the same 
   conditions, i.e., the CO total column can also be determined, and 
   included as an additional information;

3. CO and CH4 toal column retrieval algorithms for clear sky conditions;

4. Retrieval with unknown lower surface parameters;

5. Retrieval with all relevant atmospheric constituents;

6. Algorithm with cloud discrimination ability;

7. Retrieval for undercast cloud condition;

8. Retrieval with broken cloud.

At present 1, 2, and 3 have been dealt with, and satisfactory results 
are available. These are the fundamental building blocks that are 
described in this ATBD.

The MOPITT Level 1 (L1) data and the calibrated located radiances 
obtained over the entire globe for a day, are inputs to these
algorithms. The algorithms to create the L1 data are discussed in a 
separate ATBD.