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Microwave Limb Sounder

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About MLS

MLS uses microwave emission to measure stratospheric temperature and upper tropospheric constituents. MLS also has unique capability to measure upper tropospheric water vapor in the presence of tropical cirrus, and also the cirrus ice content. These measurements are valuable for diagnosing the potential for severe loss of Arctic ozone when abundances of stratospheric chlorine will still be high, and slight cooling of the stratosphere could exacerbate ozone loss due to chlorine chemistry.

MLS is providing the first global measurements of OH, HO2 and BrO, constituents that play an important role in stratospheric chemistry. MLS is unique in its ability to provide these measurements in the presence of tropical cirrus, where important processes affecting climate variability occur. MLS also provides unique measurements of cirrus ice content.

The simultaneous MLS measurements of upper tropospheric water vapor, ice content, and temperature, under all conditions and with good vertical resolution, will be of great value for improving our understanding of processes affecting the distribution of atmospheric water, climate variability, and tropospheric-stratospheric exchange. The simultaneous measurements of dynamical tracers CO and N2O enhance the value of this data set by helping identify source regions of the air masses being observed.

MLS Science Objective

The overall scientific objective of MLS is to help improve understanding and assessment of :

Ozone Depletion
  • Emphasis on the lower stratosphere
  • Perform critical monitoring of the entire stratosphere
  • During the period when ozone is most vulnerable to destruction by chlorine
Climate Change
  • Emphasis on processes in the upper troposphere and lower stratosphere
  • For both seasonal-to-interannual and long-term climate variability
Tropospheric Ozone
  • Distribution of upper tropospheric ozone measured directly
  • Important for understanding effects of aviation and radiative forcing of climate
  • Distribution of total tropospheric ozone from TOMS - MLS , OMI - MLS
Volcanic Effects
  • Ozone depletion and climate change

MLS Parameters



Spectral bands:
At millimeter and submillimeter wavelengths.
Spatial resolution:
Measurements are performed along the sub-orbital track, and resolution varies for different parameters; 5 km cross-track x 500 km along-track x 3 km vertical are typical values.
490 kg
Duty cycle:
550 W full-on
Data rate:
100 kbps
Thermal control:
Via radiators and louvers to space as well as heaters
operating range:
10-35o C
Boresight 60-70o relative to nadir

1.5 km vertical x 3 km cross-track x 300 km along-track at the limb tangent point (instantaneous field-of-view at 640 GHz)

Pointing requirements (platform+instrument, 3s):

36 arcsec
1 arcsec per second
72 arcsec per 30 seconds
2.7 arcsec per 1/6 second
1.5 x 1.9 x 1.8 m (GHz sensor);
0.8 x 1 x 1.1 m (THz sensor);
1.6 x 0.5 x 0.3 m (spectrometer)

Key Facts

  • Passive microwave limb-sounding radiometer/spectrometer
  • Measures thermal emission from the atmospheric limb
  • Provides reliable measurements even in presence of dense cirrus and volcanic aerosol

Stratospheric Chemistry

Image of Lower Stratospheric chlorine monoxide and nitric acid from UARS MLS

MLS on Stratospheric Chemistry


Image of SO2 Injected into the Earth Stratosphere by Pinatubo Volcano

MLS on Volcanoes

El Niño

Image of UARS MLS Upper Trop Water Vapor and El Nino

MLS on El Niño

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