声光光谱仪的光谱及辐射标定方法

Abstract

Objective Imaging spectrometers based on acoustooptic tunable filters (AOTFs) are widely recognized for their rapid tuning, reliability, repeatability, and ability to change spectral channels with ease. These instruments have been extensively studied in space remote sensing and reconnaissance. Meanwhile, the spectrometers should be capable of functioning accurately over a broad temperature range to deliver precise spectral information across various operating environments. However, the spectral data accuracy is compromised by ambient temperature fluctuations, which affects the AOTF' s spectral tuning and the spectrometer' s response to radiation. The tuning relationship shift is predominantly the result of refractive index changes in the acoustooptic crystal and the velocity of acoustic waves as temperature varies, altering the acoustooptic interaction within the crystal. Similarly, the spectrometer' s radiation response drifts due to alterations in the AOTF' s diffraction efficiency and temperaturedependent changes in the performance of both electronic and optical components. Although previous studies have taken account of the temperature drift in radiation response during the radiometric calibration, it is necessary to first ensure the spectral wavelength stability in the output images, and otherwise, radiometric calibration cannot be achieved. Therefore, implementing temperature corrections during spectral calibration is essential to prevent wavelength deviations in the output images during temperature shifts, which would result in erroneous radiometric calibration.Methods We propose a spectral and radiometric calibration method for correcting temperature effects. Firstly, an AOTF tuning model that incorporates a temperature variable is built. Within this model, the relationship between the drive frequency and the optical wavelength, acoustic wave velocity, refractive index, angle of incidence, and acoustic cut angle is derived. The effect of acoustic wave velocity on the drive frequency is considered independently, and a temperature increase brings about rising acoustic wave velocity, leading to a higher drive frequency (Fig. 2). Then the effect of the refractive index on the drive frequency is considered separately, and a temperature rise leads to increasing refractive index, which also results in a higher drive frequency. Meanwhile, both crystal physical parameters are considered concerning their influence on the drive frequency and compared with the actual measured frequency. At different temperatures, the response