As a newly launched earth observing satellite of China, the GF-1 satellite is intended to be applied for land resource, agriculture, and environment protection. This satellite contains four wide field viewing cameras that have a spatial resolution of 16 m at nadir. For the application of 16 m cameras, the aerosol monitoring research need to be processed as soon as possible. This study investigated the application of dark dense vegetation to the 16 m camera of GF-1.
First, blue-only algorithm was compared with blue and red algorithm with simulation retrieval based on the ground-based measurements of the typical vegetation surface spectrum. A linear relationship exists between blue and red vegetation surfaces. Thus, compared with the blue-only algorithm, the blue and red algorithm can remove land surface influence better from the top of the atmosphere reflectance. During retrieval, atmosphere correction needs to be performed to remove false dark targets, which are caused by the decrease of Normalized Difference Vegetation Index with the increase of Aerosol Optical Depth (AOD).
Tianjin, which is located in the north of China, was selected as the area of the retrieval experiment, which was conducted from August 2013 to October 2013. The result shows that aerosol distribution can be monitored efficiently by using GF-1 16 m cameras. However, the result is partly affected by cloud and haze, which restrict the capability of these cameras. The algorithm is validated by ground-based measurements of a handheld sun photometer in the west of Tianjin and the Beijing site of AERONET. Satellite-retrieved measurements demonstrate good agreement with ground-based measurements, and the correlation coefficient is greater than 0.8.
Error analysis shows that: (1) If the viewing zenith angles of the entire image are set to the same value, the retrieved AOD error can be maximized to 0.3; (2) Calibration accuracy influences retrieved accuracy, and when the calibration error is lower than 3%, the retrieved error is lower than 10%; (3) Urban aerosol can cause a large retrieval error.