Task 136 and 137
Impact of satellite sensor calibration on the long-term trend of global aerosol products.
October 26, 2012 15:25:36
Description of Problem
Aerosols influence both the transfer of short- and long-wave radiation through the processes of scattering and absorption; this is known as the aerosol direct effect. Accurate understand of the overall radiative forcing due to aerosols is further compounded due to their high spatiotemporal variability. Satellite observations on multiple platforms have been made since the late 1970s to measure aerosol loading and optical properties and have been used to constrain various types of models as well as in atmospheric reanalyses. However, inconsistencies exist between different satellite derived aerosol products which can result in discrepancies of up to 50% in aerosol optical depth (AOD), for example [Li et. al. 2009].
Li et. al. （2009）found that differences in satellite calibrations lead to the largest discrepancies in AOD, with cloud screening, aerosol model selection, and surface effects also contributing, albeit to lesser extents. Halthore et. al.  note that, due to sensor performance degradation following launch, prelaunch calibrations are generally not valid. This is further confirmed by Xiong et. al. . Due to the weak radiometric signal of aerosols, high calibration accuracy and precision are needed as well as consistency across sensors in order to produce an accurate long-term aerosol climate data record time series [Li et. al. 2009; Cao et. al. 2008]. A linear change of -0.01/decade in aerosol optical thickness (AOT) is reported from nearly 25 years of global and monthly mean AVHRR aerosol observations [Zhao et. al. 2008].
In the current study, the impact of satellite sensor calibration on the long-term trend of global aerosol products will be assessed, with a specific focus on NASA’s MODIS instruments. Other sensors of interest to this study are NOAA’s AVHRR and NOAA/NASAs VIIRS instruments.
Scientific Objectives and Approach
The approach of assessing the impact of satellite sensor calibration on the long-term trend of global aerosol products consists of several steps:
– The AOT2 System (version 2.2), An Aerosol Retrieval System for Multi-Channel Radiometers, a universal aerosol retrieval system developed by Dr. X.-P. Zhao at NOAA, will be utilized to produce aerosol products from a variety of satellite reflectance data sets. The advantage of using the AOT2 system stems from its consistent treatment of aerosol microphysical and land surface properties in the generation of aerosol products unique to each satellite input, thus eliminating signal variations influenced by the use of different aerosol and land properties.
– As mentioned above and in the previous section, a variety of satellite reflectance data sets will be utilized. Studies will be performed using current, sensor specific calibration, as well as a variety of inter-/cross- sensor and historic calibrations.
– A comparison between MODIS and VIIRS products will be of interest due to the similar onboard calibration capabilities of all channels of these two sensors. Similarly, a comparison of each with the AVHRR product will shed light on the importance of onboard calibration capabilities. AVHRR sensors are only capable of onboard calibration of thermal channels, and aerosol products have been derived from visible channels.
– After aerosol products have been derived using the AOT2 System, a comparison with AERONET ground stations and other field campaigns will provide a ground truth to which the various satellite derived aerosol products can be compared.
Work on the current study is in its infant stages. A review of relevant, peer-reviewed literature has been performed by A. Jongeward. Currently, A. Jongeward is reading documentation on and familiarizing himself with the AOT2 system. A conference presentation of current work and progress is expected during the current year.
Refereed Journal Publications
Cao, C. et. al. 2008. Assessing the consistency of AVHRR and MODIS L1B reflectance for generating Fundamental Climate Data Records. Journal of Geophysical Research. vol. 113. D09114. doi: 10.1029/2007JD009363.
Halthore, R.N. et. al. 2008. Role of Aerosol Absorption in Satellite Sensor Calibration. IEEE Geoscience and Remote Sensing Letters. vol. 5. pp. 157-161.
Li, Z. et. al. 2009. Uncertainties in satellite remote sensing of aerosols and impact on monitoring its long-term trend: a review and perspective. Annales Geophysicae. vol. 27. pp. 2755-2770.
Xiong, X. et. al. 2010. On-Orbit Calibration and Performance of Aqua MODIS Reflective Solar Bands. IEEE Transactions on Geoscience and Remote Sensing. vol. 48. pp. 535-546.
Zhao, T.X.-P. et. al. 2008. Study of long-term trend in aerosol optical thickness observed from operational AVHRR satellite instrument. Journal of Geophysical Research. vol. 113. D07201. doi: 10.1029/2007JD009061.