Data Algorithm Theoretical Basis Document (ATBD)

Level 0 to Level 1: Abstract

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Production of Located, Calibrated MOPITT Radiances from Instrument Output Counts

The MOPITT Level-0 to Level-1 ATBD briefly outlines the Measurement of Pollution in the Troposphere (MOPITT) investigation and the physics and mathematics of the algorithms that convert the raw instrument outputs in counts into calibrated radiances and geolocate them. The inputs to these algorithms are:

• The telemetered instrument outputs, including those from the detectors, all temperature, pressure, time and angle sensors, and other monitors of instrument state and performance.
• Data on the spacecraft position and attitude as a function of time.

The algorithms described in this version of the ATBD are the Version 1 prototype algorithms. These are being developed by the Instrument Team at the University of Toronto on their facilities, where they will be used to explore different approaches to the most efficient recovery of the information from the MOPITT output data, including taking account of the instrument effects expected to be present in the flight data. Subsequently these algorithms will be incorporated in formally documented production software which will be written and tested on the NCAR Science Computing Facility (SCF). This software will then be installed at the Langley DAAC, where their operation and outputs will be verified prior to launch. These algorithms will then be applied to the data acquired in orbit during the flight phase of the program.

This first version of ATBD reflects the present status of the prototype algorithms. 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 MOPITT Level 1 (L1) data are inputs to the algorithms that retrieve vertical profiles of carbon monoxide, and total column amounts of carbon monoxide and methane. The algorithms to create the Level-2 data products are discussed in a separate ATBD. The data products are described elsewhere.

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

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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 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.