SLS | Airborne – JPL Earth Science

Status: RETIRED
Type: Limb sounder
Measurements: ClO, O3, HCl, HNO3, N

SLS

The Submillimeterwave Limb Sounder (SLS) is a heterodyne radiometer-spectrometer that measures the thermal emission spectra of gases in the Earth's upper atmosphere across a range of limb tangent altitudes. Abundance proles of stratospheric gases are inferred from these spectra using standard retrieval techniques.

The current instrument measures in the 600 to 700 GHz spectral interval using an NbTi superconductor-insulator-superconductor (SIS) double sideband quasioptical mixer and a broadly tunable local oscillator. The radiometric system noise temperature of the receiver system is approximately 280 K at IF band center. The down-converted 4 GHz wide IF band is spectrally resolved and power detected using analog filterbanks and digital spectrometers.

Instrument optics provide a field-of-view full width at half maximum of 0.3 degrees to achieve vertical resolution of 1.5 km at 25 km tangent height. of the balloon platform which is typically 38 km. In flight, a full limb scan with calibration views is completed in approximately 300s. This short scan period provides profiles with sufficient temporal resolution to examine the diurnal varying gases through sunrise and/or sunset.

Spectral lines of a large number of key atmospheric gases are within the region measured by SLS. These include 35ClO, 81BrO, H35Cl, H37Cl, O3 and isotopologues, HO2, HNO3, CH3CN, HO35Cl, CH3Cl and H2O. The SLS was developed under support from the NASA Upper Atmosphere Research Program in 1989 as a successor to the Balloon Microwave Limb Sounder (BMLS), a balloon 200 GHz receiver for ClO and O3.