Compact high-resolution echelle-AOTF NIR spectrometer for atmospheric measurements

摘要

A new concept of a high-resolution near-IRrnspectrometer consisting of an echelle grating combinedrnwith an acousto-optic tunable filter (AOTF) forrnseparation of diffraction orders, is developed for spacebornernstudies of planetary atmospheres. A compactrndesign with no moving parts within the mass budget ofrn3-5 kg allows to reach the resolving power λ/Δλ ofrn20000-30000. Only a small piece of spectrum in highrndiffraction orders can be measured at a time, but thanksrnto flexibility of the AOTF electrical tuning, such piecesrnof spectrum can be measured randomly and rapidlyrnwithin the spectral range. This development can be usedrnfor accurate measurements of important atmosphericrngases, such as CO_2 in terrestrial atmosphere, isotopicrnratios and minor gases. A spectrometer, based on thisrnprinciple, SOIR (Solar Occultation InfraRed) is beingrnbuilt for Venus Express (2005) ESA mission.rnInstruments based on this principle have high potentialrnfor the studies of the Earth, in particular forrnmeasurements of isotopes of water in the lowerrnatmosphere, either in solar occultation profiling (tangentrnaltitude <10 km), or observing solar glint for integralrnquantities of the components. Small size of hardwarernmakes them ideal for micro-satellites, which are nowrnagile enough to provide necessary pointing for solarrnoccultation or glint observations. Also, the atmospherernof Mars has never been observed at local scales withrnsuch a high spectral resolution. A laboratory prototypernconsisting of 275-mm echelle spectrometer withrnHamamatsu InGaAs 512-pixel linear array and thernAOTF has demonstrated λ/Δλ≈30000 in the spectralrnrange of 1-1.7 μm. The next set up, covering thernspectral ranges of 1-1.7 μm and 2.3-4.3 μm, and thernVenus Express SOIR are briefly discussed.