Radiomeric and Geometric Analysis of Worldview-2 Stereo Scenes

Abstract

WorldView-2 (WV-2) is DigitalGlobe's latest very high resolution optical sensor. Launched on October 8, 2009 and full operational since January 5, 2010, it flies along a sun-synchronous orbit at an altitude of 770km. The sensor is able to acquire panchromatic imagery at 0.46m ground resolution (0.52m at 20° off-nadir) and multispectral images in eight spectral bands at 1.8m resolution. In addition to the four typical multispectral bands (blue, green, red, near infrared), the sensors scans in the coastal (400-450nm), yellow (585-625nm), red edge (705-745nm) and near infrared-2 (860-1040nm) bands. Stereo images can be planned thanks to the ability of the sensor to rotate off-nadir up to +/-45°. This paper describes the investigations on WV-2 that are carried out at the EU Joint Research Center (JRC) in Ispra (Italy), by the ISFEREA Team of the Istitute for the Protection and Security of the Citizen (IPSC). The purpose of the study is to evaluate the radiometric and geometric properties of the sensor and its potentials for 3D information extraction. The images used for the analysis are a stereopair over North-West Italy, where ISFEREA has established a testfield. The radiometry of the images is evaluated through different methods, including the estimation of the noise level (standard deviation of the digital number) in homogeneous and non-homogeneous areas. The images are oriented with an RPC-based approach: using GCP (ground control points), the given Rational Polynomial Coefficients (RPC) are improved with an affine transformation to compensate residual systematic errors. The achieved accuracy is investigated by varying the number and distribution of GCPs. For automatic 3D information assessment, Digital Surface Models (DSM) are generated with different commercial software available at JRC and compared with reference data. The processing steps are described in the paper and the results discussed in detail.