Measuring Inter-Band Spatial Separation by Using Cross-Correlation Operation
Miss Li-Hsueh Chang, Mr. Ming-Fu Chen, and Dr. Nai-Yu Chen
National Space Program Office (NSPO)
National Application Research Laboratories,
8F, 9 Prosperity 1 st Road
Science-Based Industrial Park, Hsin-Chu City, Taiwan, R.O.C.
TEL: 886-3-5784208 FAX: 886-3-5799972
Email: LHChang@nspo.org.tw,
Blake@nspo.org.tw,
nychen@nspo.org.tw
ABSTRACT Push-broom mechanism has been employed successfully in several remote
sensing satellite programs, including the ROCSAT-2. To simplify the instrument architecture,
CCD arrays configured with along-track pointing deviations are usually utilized in a
push-broom device for acquiring image data of different spectral ranges. As a result, inter-band
spatial separation presents. The artifact is usually removed with a band-to-band registration
operation performed in image pre-processing phase. To ensure a proper band-to-band
registration, knowledge regarding CCD pointing deviation is essential.
A cross correlation-based algorithm is proposed in this work for finding CCD pointing deviation.
Patches are first selected from the image. Follows, cross-correlation, image resampling, and
correlation interpolation are applied to detect inter-band spatial separations. From which, the
CCD pointing deviations are deduced accordingly. To examine the proposed algorithm, a
validation scheme is also developed in this work. By using a number of simulated data sets, we
validated that the proposed algorithm is capable of detecting reliably the inter-band spatial
separation with an accuracy around 0.1 ~ 0.2 pixel. It is noticed however to achieve such level
of accuracy, factors such as terrain variations, surface canopy should be counted in. Applying
the purposed algorithm on ROCSAT-2 data, the preliminary results show that the inter-band
spatial separation is close to the pre-launch measurement. Yet, systematic residual presents. A
refinement on CCD pointing model has been performed accordingly, which leads the inter-band
spatial separation of ROCSAT-2 products to an order within 0.2 pixels.
1.0 INTRODUCTION
Launched in May 2004, the Remote Sensing Instrument (RSI) on board the ROCSAT-2 satellite
acquires Panchromatic (PAN) and 4 bands of Multi-Spectral (MS) images. Due to focal plane
CCD array configuration, inter-band spatial separation is expected for those image lines. Though
the pre-launch measurement has provided the CCD pointing information, there is still a need of
examining on orbit the inter-band spatial separation, and also to refine the geometry parameters
of RSI.
A cross correlation-based algorithm is therefore developed for measuring the inter-band spatial
separation. By taking into account the influence of satellite motion, attitude change, Earth
rotation and so on, the CCD pointing is further refined according to measurement results.
