MicroMAPS is a gas filter correlation radiometer capable of detecting trace atmospheric gases by remotely sensing their infrared absorption characteristics. While the method can be used to detect a number of trace species (including CH<SUB>4</SUB>, SO<SUB>2</SUB>, and NO<SUB>2</SUB>), the current version of MicroMAPS detects CO and N<SUB>2</SUB>O from a nadir viewing orbital platform. To do this, the instrument is equipped with CO and N<SUB>2</SUB>O gas cells and configured to observe the earth's IR radiance in a band centered at 4.67 microns. It has been demonstrated that the synchronous detection of alternatively chopped signals through CO, vacuum and N<SUB>2</SUB>O view cells can produce a quantitative measure CO in three tropospheric layers. The simplicity of the method affords a low cost technique for generating global maps of this important atmospheric species when viewing from space. MicroMAPS uses the sam method of detection of trace CO as an older instrument called MAPS. MAPS (the measurement of air pollution from satellites) has heritage from shuttle missions in 1982, 1984, and 1994 (STS-2, STS-41G, and STS68). There are two fundamental differences between MicroMAPS and MAPS. To give the correlation signal related to the CO column density in the atmosphere, MicroMAPS employs a rotating gas cell chopper and a single IR detector. MAPS employs fixed gas cells with more than one detector. MicroMAPS replaces the complex amplifier and synchronous detector analog signal processing system of MAPS with a microprocessor based signal processor. The effect of these two changes reduces the weight from 100 lbs plus (MAPS) to approximately 14 lbs (MicroMAPS) as well as reducing the cost of MicroMAPS by about the same proportion as its mass. On June 8, 1994 CTA Incorporated of Rockport, Maryland was awarded a NASA contract to build the Clark spacecraft as part of the small satellite technology initiative program. In March 1995 Resonance Ltd. received a contract to build a spacequalified MicroMAPS remote sensor for this small satellite.
The importance of calibration subsystems as part of overall system design has grown with the increasing sophistication and complexity of remote sensing and imaging instruments. In general they provide spectral and radiometric reference data in-situ under remote and sometimes unpredictable instrument conditions which are used to correct electronic, optical and detector nonlinearities. The recent difficulties with GOES satellites underline the importance of reliable calibration sources for space applications. Although the calibration component is a small fraction of the budget of any space qualified instrument, its failure can result in a catastrophic loss of data. A group of sources will be described which have been developed for in-flight and pre-flight calibration of a variety of space astronomy and space physics experiments with different requirements in terms of wavelength coverage, power budget, size requirements and radiation hardness.