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MLS is the first satellite experiment to use microwave limb sounding techniques.
A 1.6 m scanning antenna views the atmosphere in the spectral bands centered at
63, 183, and 205 GHz. The MLS instrument is designed to investigate the chemical
composition of the upper atmosphere on a global scale, both day and night, over
several years.
MLS data
are available from the
Goddard Space
Flight Center (GSFC) Distributed Active Archive Center (DAAC).
-
Revision Date:Fri May 10 11:49:22 EDT 2002
03 April 1995
- Review Date:
03 April 1995
- Instrument Long Name, Acronym:
- Microwave Limb Sounder, MLS
- Instrument Introduction:
- The Microwave Limb Sounder (MLS) is one of ten instruments on NASA's
Upper
Atmosphere Research Satellite (UARS). MLS is the first experiment to use
microwave limb sounding techniques.
- Instrument Mission Objectives:
- The measurement objectives of the MLS instrument are chlorine monoxide
(ClO), ozone (O3), water vapor (H2O), temperature and pressure in the
stratosphere and mesosphere. A major emphasis is to investigate
the relationship between chlorine monoxide and ozone destruction. Simultaneous
measurements of ozone and wator vapor will also add to the understanding of
stratospheric ozone chemistry. Measurements of water vapor and ozone at
higher altitudes than previously studied will give information about chemistry
in the mesosphere. Secondary measurement objectives include H2O2, HNO3,
and volcanic injections of SO2.
- Key Variables:
- The measured parameters are temperature, and volume mixing ratios of
chlorine monoxide, ozone (at the 183 GHz and 205 GHz bands), and water vapor.
The units of measurement are parts per million by volume (ppmv) for chemical
species concentrations, and degrees Kelvin for temperature.
- Scanning or Data Collection Concept/Principles of Operation:
- The MLS instrument consists of a 1.6-m scanning antenna system, three
radiometers in spectral bands centered at 63, 183 and 205 GHz, optical
multiplexers, and an internal calibration system. The antenna scans in the
vertical over the altitude range of 5 to 90 km every 65.536 seconds.
A switching mirror inside the radiometer box selects either the atmospheric
signal from the antenna system, the calibration from an internal source,
or a zero-reference space view. The signals from the switching mirror are
then separated to the 63, 183 and 205 GHz radiometers. Next, the radiation
is downconverted to intermediate frequency (IF) bands in the 0-3 GHz range.
The IF signals are amplified and further converted to six 510 MHz wide spectral
bands, each centered at 400 MHz. The bands are then input to six filter banks
(O2 from 63 GHz; ClO, H2O2, and O3 from 183 GHz; H2O, and O3 from 205 GHz)
where the signals are split into 15 contiguous spectral channels. The power
received in each channel is integrated, and the signals are then transmitted
to Earth. The resolution of individual channels varies from 128 MHz on the
edge to 2 MHz near the center of the spectral line being measured.
- List of Sensors:
- The MLS instrument has three assembly units: spectrometer, power supply,
and the main sensor. The sensor includes the scanning antenna, the radiometer
box, multiplexing optics, and the calibration system.
- Sensor Descriptions:
- Antenna:
The antenna subsystem is a dual-offset Cassegrain consisting of three elliptical
reflectors. The primary reflector is an offset paraboloid, 1.6 x 0.8 meters,
with a 1 meter focal length. The secondary reflector is hyperboloid with
dimensions 0.45 x 0.24 meters, and the flat tertiary reflector sends the
radiation into the radiometer module. The antenna is scanned in the vertical
in discreet steps from about 5 km to 95 km, every measurement cycle of 65.536
seconds.
Radiometers:
There are three radiometers in spectral bands centered at 63, 183 and 205 GHz.
The 205 GHz radiometer is a single-ended fundamental mount based on the design
by Archer and Mattauch [1981] with a GaAs Schottky diode. The 205 GHz
radiometer measures the signal from the chlorine monoxide/hydrogen peroxide band
and ozone band. The 183 GHz radiometer is basically the same as the 205 GHz
radiometer. The 183 GHz radiometer measures the signal from the water vapor
and ozone bands. The 63 GHz radiometer is a space-qualified commercial mixer-
amplifier module using a pair of Schottky barrier diodes. The 63-GHz radiometer
measures oxygen to determine atmospheric temperature.
Optical Multiplexer:
The optical multiplexer separates the radiation from the switching mirror into
the three radiometers. The 63 GHz beam is separated with a dichroic plate
consisting of equally spaced circular holes in a metal plate. The 183 and 205
GHz beams are separated by a polarization grid of finely spaced wires.
Internal Calibration:
The MLS onboard calibrations are performed by allowing the switching mirror
to direct the radiometer FOVs to view both cold space and an internal ambient
blackbody calibration target during each limb scan.
- Sensor/Detector Specifications - Optics and Spacing:
-
Primary mirror 1.6 m
Vertical FOV 0.05 degrees
Spectral frequencies 63 GHz, 183 GHz, 205 GHz
Instrument:
Jet Propulsion Laboratory, Pasadena, California
183 GHz radiometer subsystem:
Heriot-Watt University and Rutherford Appleton Laboratory, U.K.
The MLS onboard calibrations are performed by allowing the switching mirror
to direct the radiometer FOVs to view both cold space and an internal ambient
blackbody calibration target during each limb scan (every 65.536 seconds).
- INSTRUMENT
- An integrated collection of hardware containing one or more sensors
and associated controls designed to produce data on an environment. MLS is a
single sensor instrument.
- SENSOR
- A device which transmits an output signal in response to a physical
input stimulus (as radiance, sound, etc.). The MLS sensor measures atmospheric
radiation in the microwave region.
ClO chlorine monoxide
FOV field of view
GaAs gallium arsenide
GHz Giga-hertz
H2O water vapor
H2O2 hydrogen peroxide
HNO3 nitric acid
km kilometer
m meter
MHz Mega-hertz
MLS Microwave Limb Sounder
O3 ozone
ppmv parts per million by volume
SO2 sulfur dioxide
UARS Upper Atmosphere Research Satellite
NAVIGATION BUTTONS
Change History
- Version 2.0
- Version baselined on addition to the GES Controlled Documents List, April 3, 1995.
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Atmos Composition
