High Resolution Sensor Specific Parameter Evaluation Using Cartosat-1 Imagery

The launch of Cartosat-1 is the beginning of yet another series of satellite mission after IRS satellites for earth observation and natural resource management applications. The first in its series of satellite for Cartographic applications, Cartosat-1 was launched on 5th May 2005. The along-track stereo viewing capability was realized by employing two cameras viz. FORE with mounting pitch angle of 26deg and AFT with that of –5deg with respect to nadir. The camera-mounting angle combined with the agility of camera in Roll, Pitch and Yaw direction to achieve better revisit created blend of viewing geometries. The Chharodi test site with its known dimension and artificial targets with controlled time-invariant radiometric properties were used to evaluate sensor specific parameters under these viewing geometries. Modulation Transfer Function, Square Wave Response, Point Spread Function and adjacency effect parameters were evaluated for FORE and AFT cameras. Along and across track spatial resolution were evaluated using Ground measured length, width and orientation of each side of test site using GPS in DGPS mode 1.0 INTRODUCTION After successful development of high spatial resolution satellites like TES and IRS-P6, the plausible next step was a mission with stereo viewing capability. The stereo imaging can be accomplished in more ways than one: a) in across track direction by imaging same area in different orbits by tilting camera in across track direction, b) using two camera with different fixed mounting angle in along track direction c) Along track tilting of single camera to view the same region from two different angles. The accuracy of height information derived from stereo imaging using former method can be adversely affected as these images are acquired on different days during which the atmospheric condition may not remain constant. The objective of this analysis is to validate high-resolution sensor parameters using calibrated ground targets. The continuous improvement in GSD, mission to mission, requires close monitoring of parameters like spatial resolution and radiometry, important for mapping satellites . During this study following radiometric and geometric parameters were analyzed. a) Ground measured length, width and orientation of each side of test site using GPS in DGPS mode. b) Computation of frame length, swath width and orientation of each side of test site as Along & Across track distance using Stereo pair and Georeferenced image data. c) Derivation of Along and Across track spatial resolution using aforesaid parameters. d) At sensor target mean count, standard deviation, radiance and Apparent Reflectance e) Point Spread function from specially designed PSF targets f) Square wave response for various frequencies, (Along and Across scan). g) Edge-based Modulation Transfer function h) Adjacency Effect 2.0 CARTOSAT-1 CONFIGURATION Cartosat-1 satellite, the first dedicated stereo imaging mission [2] by ISRO, was launched on 5 May 2005. The payload performance specification for CARTOSAT-1 mission is listed in Table 1. Sr. No. Parameter Specification 1 Spatial Resolution (m) at Nadir 2.5m 2 Swath (km) Fore Aft Swath steering Range 30Km 27.5Km 131Km(+/-12deg) 3 Spectral Bands (μ) .50 .75 4 Camera SWR at Nyquist Freq. >.20 5 F Number Height Resolution f/4.5 4.0 Meters 6 Quantization 10 Bits 7 SNR (at sr.) >64 8 Saturation Radiance 53.46 mw/cm/sr/μ 9 Integration Time 365.71 μs 10 No of output Ports 8 11 Data Rate (mbps) 2 x 52.5 Table: 1 Payload Performance Parameters The satellite with along track stereo imaging capability and dedicated to cartographic applications, CARTOSAT-1, uses two Panchromatic camera operating in spectral band 0.50.85μm with spatial resolution of 2.5m each, mounted with +26deg pitch angle (named FORE) and another mounted in –5.0deg pitch angle (named AFT) to generate along track stereo images. The swath coverage is 30km. The two identical PAN cameras cover dynamic range of 100% albedo with 10bit radiometric quantization, suitable for cartographic applications. The CCDs of size 7μm x 7μm forms an array of 12k CCDs with odd/even pixels separated into two rows to avoid electronic cross-talk effect on adjacent pixels . This arrangement is to improve Modulation Transfer Function at detector level. Over and above the mounting angles of FORE