Comparison of MAS and HIS Observations

The following figure compares averages of MAS 5x7 groups of pixels near nadir (solid line) with HIS radiances averaged over the half-power points of the MAS (squares). This comparison (made in equivalent brightness temperatures) was conducted to check that the MAS and HIS clocks and navigation are in agreement. The MAS image at the top of the figure is the 1.88 micron channel.

The high spectral resolution and accurate calibration of the HIS allows for vicarious calibration of the MAS infrared channels. To accomplish this comparison the HIS spectra are integrated over the MAS spectral bandpass and the MAS radiance observations are averaged over the field of view of the HIS. The radiances are then converted to a brightness temperature and compared with one another. The figure below demonstrates this comparison for the 11 micron band of the MAS using observation collected on April 13 and 15. The different symbols represent different standard deviations of the MAS radiances within the HIS footprint. The noise equivalent temperature of the MAS 11 micron channel is 0.1 degrees at 293K. Much of the variability in the HIS fov is due to variations associated with the scene. Vicarious calibration of the MAS is conducted only over uniform scenes (see Gumley, van Delst and Moeller).