Armenakis & Savopol 23 MAPPING POTENTIAL OF THE IRS-1C PAN SATELLITE IMAGERY Costas Armenakis and Florin Savopol Centre for Topographic Information (CTI) Geomatics Canada 615 Booth Str., Ottawa, Ontario, Canada K1A 0E9 Tel: (613) 992-4487; Fax: (613) 947-7948 E-mail: {armenaki} {fsavopol}@nrcan.gc.ca Keywords: IRS-1C, PAN camera, satellite imagery, orthorectification, monoscopic-mode, topographic mapping. ABSTRACT The current and upcoming high resolution satellite imagery is expected to have a significant impact on the topographic mapping applications of primary data acquisition and especially on the updating of databases. The Centre for Topographic Information (CTI), Geomatics Canada has initiated an investigation to evaluate the use of space imagery in the national topographic program from technical, systems and economic points of view. For this purpose a scene and the three CCD scenes from the PAN camera of the Indian Remote Sensing satellite IRS-1C were acquired covering the east of Ottawa region. The initial tests conducted aimed to examine the geometric and radiometric characteristics of the imagery, the detectability and identification of topographic features for data collection and database updating, as well as the suitability of the existing system and the determination of additional requirements. The performance of existing line scanner sensor modelling was tested on the entire IRS-1C scene, on a sub-scene consisting of segments from the three image arrays and on an array sub-scene. Orthoimages were produced from contour generated DEM and geometrically tested. Extraction and classification of topographic features were evaluated from the orthoimagery in a monoscopic mode. For 1:50000 mapping, initial results showed that the imagery can meet the accuracy requirements and when contextual information is available has the potential to support the updating of certain features in new suburban developments and in non urban areas,. 1 INTRODUCTION The Indian Remote Sensing satellite IRS-1C was launched in December 1995 and carries three sensors. One of them is the PAN camera, a panchromatic sensor with 5.8m spatial resolution and 6-bit (64 grey levels) radiometric resolution. It consists of three CCD linear arrays with 4096 pixels each and covers a swath of about 70km (3x23.3km or approximate 12000 pixels). The dimension of each pixel is 7 micrometers. The three sensors overlap but are neither parallel nor aligned (Srivastava and Alurkar, 1997; Jacobsen, 1998). The configuration of the three CCD sensors on the image plane is illustrated in Fig. 1. The overlap between CCD1 and CCD 2 is 243 pixels and between CCD 2 and CCD 3 is 152 pixels. The nominal focal length of the PAN camera is 982mm. The IRS-1C satellite is on sun synchronous orbit with an inclination of 98.69 degrees, an attitude of 817km, repetivity of 24 days, local time of imaging at about 10:30am and revisit of 5 days (Shivakumar et al., 1996). The latter as well as stereoscopic across track coverage are accomplished by a rotation of the entire PAN camera up to +/-26 degrees. When marketed, the IRS-1C is resampled to 5m and the three array images are mosaicked to form a scene that covers an area of 70kmx70km. As well the radiometric resolution is scaled to 8-bit quantization levels (256 grey levels). The individual image arrays (left, middle and right) can be obtained as well. Because of its high spatial resolution, the IRS-1C PAN imagery is of significant interest for topographic mapping applications such as primary data collection and database revision and updating. The Centre for Topographic Information (CTI) has utilized digital orthoimages from aerial photography (Armenakis et al., 1995) and SPOT panchromatic imagery (Savopol, 1994) for updating of the National Topographic Database (NTDB) in a monoscopic mode. Because of cost and spatial resolution, CTI acquired an IRS-1C PAN scene to use in a similar mode and evaluate its geometric and radiometric properties. For this investigation the 287/037 scene, taken on November 25, 1996, and its three individual sub-scenes were acquired. The scene covers the east of Ottawa area. The scene is of nadir view (1.96 degrees). Although this scene was not ideal because of the low sun angle of 23.3 degrees, this scene was selected as being free of clouds and snow coverage at the time of image selection. The evaluation of the existing systems in CTI in using the IRS-1C imagery and determination of additional requirements, if any, are included within the scope of this investigation. Figure 1: IRS-1C PAN camera configuration (not to scale).    152 pixels 243 pixels 4096 pixels 4096 pixels 4096 pixels    152 pixels 243 pixels 4096 pixels 4096 pixels 4096 pixels D. Fritsch, M. Englich & M. Sester, eds, 'IAPRS', Vol. 32/4, ISPRS Commission IV Symposium on GIS - Between Visions and Applications, Stuttgart, Germany.