The UARS MLS instrument is described by Barath et al. [ J. Geophys. Res., vol. 98, pp. 10,751-10,762, 1993] and its calibration by Jarnot et al. [ J. Geophys. Res., vol. 101, pp. 9957-9982, 1995]; these papers can be consulted for more information than given in the brief summary here.
Photo & Sketch
The figures below show a photo and sketch of UARS MLS. The instrument has three assemblies: sensor, spectrometer and power supply. Thermal control of the sensor is radiational by louvers, with in-orbit temperature stability of approximately 0.01oC or better, allowing "total power" measurements which do not require fast switching to a reference. The overall instrument mass is 280 kg, power consumption is 163 W fully-on, and data rate is 1250 bits/second.
A signal flow block diagram of the instrument is shown below.
The IF signals, after amplification, are further frequency-converted to six spectral bands, each centered at 400 MHz with approximately 500 MHz instantaneous spectral bandwidth. These bands are input to six filter banks which split the signal into 15 separate filter channels, simultaneously measure the power in each of these channels, and digitize the resulting signals to pass along to UARS for transmission to the ground and data processing.
All measurements are, under normal operation, performed continuously day and night. The instrument integration time is approximately 2 seconds.
MLS looks in a direction which is 90° from the UARS orbital velocity, and the tangent point of the observation path (where the signals mostly originate) is 23 great-circle degrees away from the suborbital path of the satellite. The 57° inclination of the UARS orbit thus allows MLS to perform measurements from 34° on one side of the equator to 80° on the other. UARS performs a 180° `yaw maneuver' ten times per year, allowing MLS to alternate between views of northern and southern high latitudes at approximately 36-day intervals (this varies a few days through a yearly cycle). Local solar times at measurement locations do not vary appreciably with longitude on a given day, but can vary greately with latitude on a given day.
The figures below show a photograph of UARS during ground tests before launch, and a sketch of UARS in orbit; MLS is seen in these figures near the righthand side of UARS.