GEOMETRY AND RADIATION QUALITY EVALUATION OF GF-1 AND GF-2 SATELLITE IMAGERY. Yong Xie

Transcription

1 Prepared by CNSA Agenda Item: WG.3 GEOMETRY AND RADIATION QUALITY EVALUATION OF GF-1 AND GF-2 SATELLITE IMAGERY Yong Xie Institute of Remote Sensing and Digital Earth, Chinese Academy of Science GF-1 and GF-2 are the first two satellites of China High-resolution Earth Observing System (CHEOS). Both two satellites have been used in diversities application areas, such as land resource and surveying, disaster mitigation, environment protection, and so on. In this paper, the result of geometry and radiation quality evaluation of GF-1 and GF-2 satellite imagery is reported.

2 Geometry and Radiation Quality Evaluation of GF-1 and GF-2 Satellite Imagery 1 INTRODUCTION GF-1 and GF-2 satellites are the first two satellites in CHEOS (Chinese highresolution earth observation system). Their imageries have been applied wildly in many fields, such as resources survey, environmental monitoring, and disaster mitigation and so on. As the high-resolution satellites, the users and researchers pay more attention to the geo-positioning and radiation precision of those imageries. In this report, the geometry and radiation evaluation of two satellite imagery are evaluated. 2 GEOMETRY QUALITY EVALUATION OF GF SATELLITE IMAGERY 2.1 Geometry quality of GF-1 satellite imagery For the GF-1 satellite, the geo-positioning stability of PMS and WFV imageries are investigated by chosen ZY-3 images as the reference. The results show a clear systematic error of geo-positioning performance by using the RPC file. The average geometric offsets are approximately 60m for PMS and 100m for WFVs. Fig.1 The systematic errors of PMS2 (left) and WFV3 (right) images of GF-1 satellite. 2.2 Geometry quality of GF-2 satellite imagery For the GF-2 satellite, a bunch of GCPs are applied to evaluate the geopositioning performance. The results manifest the geo-positioning performances also exist systematic errors in each image. The average geometric errors are about 80m. P 2 f 6

3 Fig.2 The systematic errors of PMS1 (left) and PMS2 (right) images of GF-2 satellite. 3 RADIATION QUALITY EVALUATION OF GF SATELLITE IMAGERY 3.1 Radiation quality of GF-1 satellite imagery PMS sensor calibration using MODIS and OLI For PMS sensor, Landsat8/OLI is used as reference sensor. Two Spectral Band Adjustment Factors (SBAFs) are used in cross calibration which are radiance SBAF and reflectance SBAF. The uncertainty analyze results, summarized in Fig.3 and Table.1, show that the cross calibration using OLI with reflectance SBAF factor is better than radiance SBAF with uncertainty of 5-7%. Fig. 3 Cross calibration result of WFV using OLI as reference sensor Table I Calibration uncertainty of cross calibration using OLI with reflectance SBAF factor blue green red NIR Ground reflectance 2.81% -1.97% 1.87% -4.56% Atmosphere 6.14% 4.04% 2.98% 3.02% Reference sensor 2% 2% 2% 2% Site homogeneous 0.50% 0.50% 0.50% 0.50% Direction reflectance 1% 1% 1% 1% Other uncertainty 1% 1% 1% 1% Total uncertainty 7.2% 5.14% 4.32% 6.01% P 3 f 6

4 WFV sensor calibration using OLI CGMS-43 CNSA-WP-05 For WFV sensor, Landsat 8/OLI was used as reference sensor. Three cross calibration methods which are one-point method, multi-point method and whole image method are used for cross calibration of GF-1 satellite WFV 4 sensor, taking Landsat 8 OLI as reference sensor. The results (Fig.4) show that the one-point method has the highest calibration accuracy with the uncertainty of 5.85%. Fig.4 Calibration accuracy of three methods 3.2 Radiation quality of GF-2 satellite imagery Radiation quality validation with in-situ measurement The GF-2 calibration was still carried out with in-situ measurements at Dunhuang calibration site. The validation is performed at a semi-dry salt lake named Shah Baltu playa which is located in inner Mongolia with the geolocation of N and E and the altitude of 1400m. Shah Baltu playa is a flat area with half water and half dry salt. Its coverage is up to 800x800m. Fig. 5 shows the GF-2 multi-spectral false color image of Shah Baltu playa site and ground photo imaged by camera in situ. Three ROIs (Region of Interest) are chosen to validate the calibration official coefficient. As shown in Fig.5 1, the green and blue square denotes the ROI1, and ROI2, which are dry salt soil, and the red square is presented the ROI3 of wet salt soil. The ground reflectance of these ROIs is measured using SVC spectrometer. Fig.6 shows the mean reflectance of each ROI. It can be found that the reflectance of ROI1 and ROI2 are much close as they are both dry salt soil, while the ROI3 s reflectance is much lower than ROI1 and ROI2. The comparison between simulated radiance (simulated by inserting in-site measured reflectance into MODTRAN) and GF-2 calculated radiance is shown in Fig.7. In the figure, five dots in same colour P 4 f 6

5 represents four-band multi-spectral and panchromatic band. The CWs of multispectral and panchromatic band are nm, 555,38nm, nm, nm and nm. The results show that in ROI1 and ROI area, simulated radiance and GF- 2 calculated radiance are much closer and the calibration coefficient of PMS can be used in deriving the radiance product. Also, it is found that there is a large difference in blue band at ROI3, which is might due to the mis-registration and ground measure error. Fig. 5 GF-2 PMS image over the Shah Baltu playa Fig.6 Ground reflectances of three ROIs over the Shah Baltu playa Fig. 7 Radiance comparison between simulated radiance based on ground reflectance and MODTRAN Model and image radiance based on calibration coefficient. Evaluation of GF-2 PMS linearity with Landsat 8 OLI Landsat 8 OLI sensor is used to evaluate linearity of GF2 PMS. An image pair of PMS and OLI image are imaged at Inner Mongolia, China on December 30, P 5 f 6

6 ROIs are chosen in both PMS and OLI image. The ground types of 12 ROIs include water, withered grass, salt soil, ice sheet et al. The OLI radiance and PMS radiance over each ROI are computed according the calibration coefficient. Then the OLI radiance and PMS radiance are plotted to calculate the linearity. The transfer formulate between OLI radiance and WFV radiance are computed using the least square method and the linearity is also calculated according the correlation coefficient. As the results shown in Table 2, it is found that the PMS has a good linearity with OLI. Table 2 Radiance transfer formation and linearity Camera Band Transfer Formulate* Linearity PMS and OLI MSS1 PMS = OLI MSS2 PMS = OLI MSS3 PMS = OLI MSS4 PMS = OLI PAN PMS = OLI CONCLUSIONS Generally, the geometry and radiation quality of GF-1&2 satellite imagery is fitness. The geometric positioning accuracy of GF-1&2 satellite imagery can meet the requirement of image high precision orientation. Due to no on-board calibrator, the accuracy is depending upon the in-situ measurements of filed campaigns. The longterm cross calibration is necessary and ongoing. Page 6 of 6