Abstract
The HJ-1A and HJ-1B satellites were launched successfully on September 6, 2008. For effective monitoring of the environmental and natural disasters, both HJ-1A and HJ-1B carry a charge-coupled device (CCD) sensor, with each CCD sensor containing two cameras, which results in a ground swath of about 700 km for each satellite. The CCD can make cross-track multiple view angle measurements with a field of view of >40 deg . The Earth’s surface can be covered completely within 48 h in four spectral bands from 0.43 to 0.90 μm. We have presented a method of extracting the hemispherical-directional reflectance factor (HDRF) from CCD imagery and normalizing HDRF to a standard geometric situation. After geometric correction and registration, radiometric calibration, and correction for atmospheric effects, multitemporal HDRFs were obtained for the flat land surface located in Northern China with different land cover types. The angular observations were extracted from a series of overpasses of the CCD aboard HJ-1A and HJ-1B. We then inverted the HDRFs by the semiempirical kernel-driven bidirectional reflectance distribution function (BRDF) model and normalized the HDRFs to nadir-viewing direction. This study shows the significance of directional effects in the HJ-1A and HJ-1B CCD data and the feasibility of normalizing HDRFs’ CCD data when the angular effects must be taken into account.
Highlights
Researchers have indicated that the number and strength of extreme climate events and natural disaster events, such as storms, hurricanes, typhoons, floods, droughts, and tornadoes, have increased significantly over the past 10 to 20 years, and situations are expected to become more severe in the coming years.[1]
The HJ-1A and HJ-1B satellite sensors have the capability of sampling the hemispherical-directional reflectance factor (HDRF) over a wide range of view zenith angle in a short time period in four spectral bands from 0.43 to 0.90 μm, which makes them attractive for detecting land cover changes, vegetation dynamics monitoring, and primary production estimates
Surface HDRFs obtained in situ is essential if we want to evaluate the models in isolation from the other confounding influences and in a relatively controlled manner
Summary
Researchers have indicated that the number and strength of extreme climate events and natural disaster events, such as storms, hurricanes, typhoons, floods, droughts, and tornadoes, have increased significantly over the past 10 to 20 years, and situations are expected to become more severe in the coming years.[1]. Zhao et al.: Bidirectional reflectance effects over flat land surface from the charge-coupled device data sets. Taking into account the effect of the Earth’s surface curvature, view zenith angles of up to þ47 deg from the nadir have been sampled in this study. Because the HJ-1A and HJ-1B satellites are in the same orbit with a phase difference of 180 deg, the repeat cycle of the CCD sensor is reduced to
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