Spatial Heterodyne Imager for Mesospheric Radicals on STPSat‐1

Abstract

[1] The Spatial Heterodyne Imager for Mesospheric Radicals (SHIMMER) was a high-resolution, near ultraviolet spectrometer that imaged the Earth's limb for 2.5 years between March 2007 and October 2009. The instrument used the Spatial Heterodyne Spectroscopy technique for the first time on a satellite and successfully demonstrated its capabilities. SHIMMER measured the solar resonance fluorescence of the OH A 2 S + -X 2 P (0, 0) band around 309 nm, which allows the retrieval of mesospheric OH density profiles. It also measured the Rayleigh scattered background from the clear atmosphere and solar scattering from polar mesospheric cloud particles. We present details on the SHIMMER mission, the payload design, and the data analysis. A comparison between SHIMMER and concurrent Microwave Limb Sounder OH data shows good agreement between 60 and 90 km altitude for several latitudes and seasons. We also find good agreement of the SHIMMER OH densities and standard photochemical model calculations between 60 and 80 km. We find no evidence of a 25%-35% mesospheric OH deficit, previously reported using Middle Atmosphere High-Resolution Spectrograph Investigation (MAHRSI) OH data. However, independent analysis of Rayleigh scattered background signals observed by SHIMMER and MAHRSI under similar lighting conditions revealed that MAHRSI radiances are systematically smaller than SHIMMER radiances by 24%. Although this difference is well outside of the combined uncertainties for both experiments, the agreement of SHIMMER OH with Microwave Limb Sounder OH and standard photochemistry results, together with our Rayleigh scattering comparison, suggests an unidentified MAHRSI calibration problem that effectively eliminates the mesospheric OH deficit reported using MAHRSI observations.

Comparison of a photochemical model with observations of mesospheric hydroxyl and ozone

“…Taken together, the net effect of these changes is to reduce the calculated OH by about 6% as compared with our calculations in Englert et al . []. While this difference is small, since the calculated OH was already about 10% lower than the observations in the Englert et al .…”

“…Thus, first results from the Spatial Heterodyne Imager for Mesospheric Radicals (SHIMMER) [ Englert et al ., ] and the Aura Microwave Limb Sounder (MLS) [ Pickett et al ., ] found good agreement between their data and models. Englert et al [] presented arguments that the MAHRSI data may have had an unidentified calibration problem which led to the somewhat lower values of hydroxyl abundance first reported by Summers et al . [] and concluded that there is no model overprediction of mesospheric odd hydrogen.…”

Consequences of recent Southern Hemisphere winter variability on polar mesospheric clouds

“…Section 2 presents 3 NH seasons of mesospheric cloud data from two instruments, the Solar Occultation for Ice Experiment (SOFIE) and the Spatial Heterodyne Spectrometer for Mesospheric Radicals (SHIMMER). SOFIE is on board the NASA Aeronomy of Ice in the Mesosphere (AIM) satellite (Russell et al, 2009) (Englert et al, 2010). Both SHIMMER and SOFIE observed mesospheric clouds during the 2007, 2008 and 2009 Northern summer seasons, but, as we will discuss, using quite different observational techniques and from different orbits.…”

High sensitivity trace gas sensor for planetary atmospheres: miniaturized Mars methane monitor

“…More details on a technique that can be used to correct for the thermal defocus effect in an SHS instrument can be found in Ref. 15. It is worth noting that especially for high fringe frequencies, defocusing will result in a fringe contrast reduction and therefore a decrease in the signal-to-noise ratio, which cannot be recovered.…”

“…15 Both of these effects can be corrected in the data analysis if the temperature is stable during an individual exposure since (1) the spectral shape of the measured signal is known (except for the magnitude of the absorption) which allows the determination of the wavelength scale for each measured spectrum from the spectrum itself and (2) the absorption measurement is self-calibrating since the baseline is measured with each exposure. More details on a technique that can be used to correct for the thermal defocus effect in an SHS instrument can be found in Ref.…”