Moderate Resolution Imaging Spectroradiometer L1B Research Articles

A surface reflectance correction model to improve the retrieval of MISR aerosol optical depth supported by MODIS data

Combined use of different satellite sensors are known to improve retrievals of aerosol optical depth (AOD). In this study, we propose a new method for retrieving Multi-angle Imaging SpectroRadiometer (MISR) AOD data supported by Moderate Resolution Imaging Spectroradiometer (MODIS) data in Jiangsu Province, China, over the period of 2016–2018 using MODIS L1B, bidirectional reflectance distribution function (BRDF), MISR 1B2T, and ground-measured AOD data. This method is based on the surface reflectance determined by the MODIS V5.2 algorithm. Through the observation angle and spectral conversion between different sensors, the MISR AOD can be obtained. The correlation coefficient (R) and root-mean-square error (RMSE) between the retrieved MISR and ground-measured AOD data varied between different seasons. The accuracy of the MISR AOD retrieval was notably improved after correcting the MISR surface reflectance. Therefore, the method proposed in this study is feasible for the retrieval of MISR AOD supported by MODIS data, and will be applicable to atmospheric environmental monitoring over large areas in the future.

Improvements in the On-Orbit Response Versus Scan Angle Characterization of the Aqua MODIS Reflective Solar Bands

The Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) has been chosen by the Global Space-based Inter-Calibration System operational community as the reference sensor in cross-sensor calibration. A number of geostationary orbit and low-earth orbit sensors use the 0.64- $\mu \text{m}$ band from Aqua MODIS as a calibration reference. After over 15 years on-orbit, the performance characteristics of the MODIS instrument have changed, with effects evident at short wavelengths. MODIS employs a reflectance-based calibration using the solar diffuser measurements with the monthly lunar observations facilitating a response versus scan angle characterization on-orbit. As the instrument continues to operate beyond its design lifetime of 6 years, the on-board calibrators alone are insufficient to accurately characterize the instrument’s response at all scan angles. This results in a long-term reflectance drift, particularly observed in the 0.64- and 0.85- $\mu \text{m}$ bands, while observing the temporally invariant desert sites. Long-term reflectance drifts of up to 2% and 3% are observed at the beginning of scan for the 0.64- and 0.85- $\mu \text{m}$ bands, respectively. An approach using earth-view response to supplement the on-board calibrator measurements has been shown to overcome these inadequacies and is now implemented for the 0.64-, 0.85-, 0.46-, and 0.55- $\mu \text{m}$ land bands of Aqua MODIS. This paper presents the details related to the algorithm implementation and an independent evaluation using the Dome Concordia site and deep-convective clouds. This approach has been reviewed, tested, and approved by the MODIS science team and has been implemented in the forward production of the MODIS L1B Collection 6 starting July 9, 2016. This enhanced approach has also been adopted in the MODIS L1B Collection 6.1 reprocess for the entire mission to facilitate an improved quality of downstream science products. The results with the enhanced approach reduce the reflectance drifts to within 0.5% for most cases.

Evaluation of MODIS thermal IR band L1B radiances during SAFARI 2000

On 11 September 2000, a NASA ER‐2 aircraft underflew the Terra spacecraft during the Southern Africa Regional Science Initiative (SAFARI) 2000 field experiment. The Scanning High Resolution Interferometer Sounder (S‐HIS), Moderate Resolution Imaging Spectroradiometer (MODIS) Airborne Simulator (MAS), and Cloud Physics Lidar (CPL) instruments onboard the ER‐2 have provided a data set for a first look at the accuracy of the Collect 3 (L1B Version 3.X) Terra MODIS L1B radiances for the thermal infrared (TIR) bands. Based on comparisons between MODIS and S‐HIS nadir viewing data and an estimation of the existing uncertainties, the radiances of most MODIS TIR bands are found to be very near or within specification. There does not appear to be a significant influence by electronic cross talk on the midwave IR (MWIR) bands for the low reflectance, flat thermal scenes used in the evaluation. Longwave IR (LWIR) split window band residuals are within 0.1 K with an estimated uncertainty of ±0.13 K, raising confidence in their accuracy. Midtropospheric water vapor band residuals are also within specification, despite known detector striping in these bands. Residuals in the LWIR upper tropospheric CO2 bands 34–36 exceed specification. However, these are not considered strong indications of L1B performance issues due to possible undocumented uncertainty in the altitude correction for the unmeasured atmosphere above the ER‐2 aircraft level.