Korablev Oleg, Fedorova Anna, Villard Eric, Joly Lilian, Kiselev Alexander, Belyaev Denis, Bertaux Jean-Loup
Space Research Institute (IKI), 84/32 Profsoyuznaya, 117997 Moscow, Russia.
Opt Express. 2013 Jul 29;21(15):18354-60. doi: 10.1364/OE.21.018354.
Acousto-optic tunable filter (AOTF) spectrometers are being criticized for spectral leakage, distant side lobes of their spectral response function (SRF), or the stray light. SPICAM-IR is the AOTF spectrometer in the range of 1000-1700 nm with a resolving power of 1800-2200 operating on the Mars Express interplanetary probe. It is primarily dedicated to measurements of water vapor in the Martian atmosphere. SPICAM H(2)O retrievals are generally lower than simultaneous measurements with other instruments, the stray light suggested as a likely explanation. We report the results of laboratory measurements of water vapor in quantity characteristic for the Mars atmosphere (2-15 precipitable microns) with the Flight Spare model of SPICAM-IR. We simulated the measured spectra with HITRAN-based synthetic model, varying the water abundance, and the level of the stray light, and compared the results to the known amount of water in the cell. The retrieved level of the stray light, assumed uniformly spread over the spectral range, is below 1-1.3·10(-4). The stray may be responsible for the underestimation of water abundance of up to 8%, or 0.6 pr. µm. The account for the stray light removes the bias completely; the overall accuracy to measure water vapor is ~0.2 pr. µm. We demonstrate that the AOTF spectrometer dependably measures the water abundance and can be employed as an atmospheric spectrometer.
声光可调谐滤波器（AOTF）光谱仪因光谱泄漏、光谱响应函数（SRF）的远旁瓣或杂散光而受到批评。SPICAM-IR是一种工作在火星快车星际探测器上的AOTF光谱仪，工作在1000 - 1700纳米范围内，分辨能力为1800 - 2200。它主要用于测量火星大气中的水汽。SPICAM H₂O的反演结果通常低于与其他仪器的同步测量结果，杂散光被认为是一个可能的解释。我们报告了使用SPICAM-IR飞行备用模型对火星大气特征量（2 - 15可降水微米）水汽进行实验室测量的结果。我们用基于HITRAN的合成模型模拟测量光谱，改变水汽丰度和杂散光水平，并将结果与气室中已知的水汽量进行比较。反演得到的杂散光水平（假设在光谱范围内均匀分布）低于1 - 1.3·10⁻⁴。杂散光可能导致水汽丰度低估高达8%，即0.6 pr. µm。考虑杂散光后完全消除了偏差；测量水汽的总体精度约为0.2 pr. µm。我们证明了AOTF光谱仪能够可靠地测量水汽丰度，可作为一种大气光谱仪使用。
