Articles | Volume 8, issue 7
Research article
22 Jul 2015
Research article |  | 22 Jul 2015

MISR empirical stray light corrections in high-contrast scenes

J. A. Limbacher and R. A. Kahn

Abstract. We diagnose the potential causes for the Multi-angle Imaging SpectroRadiometer's (MISR) persistent high aerosol optical depth (AOD) bias at low AOD with the aid of coincident MODerate-resolution Imaging Spectroradiometer (MODIS) imagery from NASA's Terra satellite. Stray light in the MISR instrument is responsible for a large portion of the high AOD bias in high-contrast scenes, such as broken-cloud scenes that are quite common over ocean. Discrepancies among MODIS and MISR nadir-viewing blue, green, red, and near-infrared images are used to optimize seven parameters individually for each wavelength, along with a background reflectance modulation term that is modeled separately, to represent the observed features. Independent surface-based AOD measurements from the AErosol RObotic NETwork (AERONET) and the Marine Aerosol Network (MAN) are compared with MISR research aerosol retrieval algorithm (RA) AOD retrievals for 1118 coincidences to validate the corrections when applied to the nadir and off-nadir cameras. With these corrections, plus the baseline RA corrections and enhanced cloud screening applied, the median AOD bias for all data in the mid-visible (green, 558 nm) band decreases from 0.006 (0.020 for the MISR standard algorithm (SA)) to 0.000, and the RMSE decreases by 5 % (27 % compared to the SA). For AOD558 nm < 0.10, which includes about half the validation data, 68th percentile absolute AOD558 nm errors for the RA have dropped from 0.022 (0.034 for the SA) to < 0.02 (~ 0.018).

Short summary
We address mirroring, blurring, and background radiometric anomalies in the MISR standard Level 1 product empirically by comparing nadir-view near-infrared MISR with simultaneous MODIS images in high-contrast scenes. These anomalies affect aerosol optical depth and aerosol type results, especially over dark ocean scenes with broken cloud. We validate the corrections in all MISR channels by comparing multi-angle research retrievals with 1100 simultaneous surface sun photometer observations.