NASA logo

High Resolution Dynamics Limb Sounder (HIRDLS)

IntroductionImage GalleryScience Results


The HIRDLS instrument can obtain profiles over most of the globe, both day and night. Complete Earth coverage can be obtained in twelve hours. Observations of the lower stratosphere and upper troposphere are possible through the use of special narrow and more-transparent spectral channels.

After launch, activation of the HIRDLS instrument revealed that the optical path was blocked so that 20% of the aperture could view the earth's atmosphere. Engineering studies suggest that a piece of thermal blanketing material ruptured from the back of the instrument during the explosive decompression of launch. Attempts to remove this material mirror failed. However, even with the 80% blockage, measurements at high vertical resolution can be made at one scan angle.

HIRDLS stopped taking data on March 17 2008 due to failure of the chopper unit.

HIRDLS Parameters



Spectral Range:
6 to 18 mm
Standard profile spacing:
5o longitude x 5o latitude, and 1-km vertical resolution; programmable to other modes and resolutions
Spatial resolution:
Profile spacing 500 km horizontally (5o lat) x 1 km vertically; averaging volume for each data sample 1 km vertical x 10 km across x 300 km along line-of-sight
220 kg
Duty cycle:
220 W (average), 239W (peak)
Data rate:
65 kbps
Thermal control:
Stirling cycle cooler, heaters, sun baffle, radiator panel
Thermal operating range:
20o-30o C
Scan range:
Elevation, 22.1o to 27.3o below horizontal, Azimuth, -21o (sun side) to +43o (anti-sun side)
Detector IFOV :
1 km vertical x 10 km horizontal

Pointing requirements (platform+instrument, 3s ):

Control & Knowledge:
Such that scan range will allow all channels to observe from 0.25o below the hard horizon to 3.25o above it
30 arcsec /sec per axis
84-Hz sample spacing uniform to ±7 arcsec

Key Facts

  • Scanning infrared limb sounder observes global distribution of temperature and concentrations of O3 , H2O , CH4 , N2O , NO2 , HNO3 , N2O5 , CFC 11, CFC12 , ClONO2
  • Observes aerosols in the upper troposphere, stratosphere, and mesosphere

Instrument Science

Overall science goals of HIRDLS are to observe the global distributions of temperature and several trace species in the stratosphere and upper troposphere at high vertical and horizontal resolution. Specific issues to be investigated include:

  • Fluxes of mass and chemical constituents between the troposphere and stratosphere [stratosphere-troposphere exchange (STE)];
  • chemical processes, transport, and mixing [particularly in the upper troposphere/lower stratosphere (UT/LS)];
  • momentum, energy, heat, and potential vorticity balances of the upper troposphere and middle atmosphere;
  • geographically and seasonally unbiased long-term climatologies and interannual variability of middle-atmosphere temperature, constituents, dynamical fields, and gravity waves;
  • global distributions and interannual variations of aerosols, cirrus, and PSCs;
  • tropospheric cloud-top heights;
  • tropospheric temperature and water vapor retrievals (by providing high-resolution limb data for joint retrieval with EOS nadir sounders); and
  • diagnostic studies of atmospheric dynamics, chemistry, and transport processes, down to small spatial scales, to test and improve models of these processes.

Although HIRDLS lost is azimuth scanning capability, much of the science can be retained through the use of chemical transport and data assimilation models.