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Change detection of Alam-chal Glacier Surface Using Spot 5 Image Yousef Rezaei MSc of remote sensing, K.N.T University of Technology Email: y.rezaei@gmail.com M.J Valadan zouj Assistant professor, Geodesy and Geomatics Engineering Faculty, K.N.Toosi University of Technology Valiasr Av., Mirdamad Cross, Tehran, Iran Email: valadanzouj@kntu.ac.ir F. Vaziri K.N.T University Researcher Abstract Monitoring the changes of Glacier Surface can provide useful information on phenomena such as glacier motion or Glacier retreat. They can also reflect the effect of global warming on the dynamic of ice masses. Monitoring of Glacier motion is one of the key issues to glacier dynamics understanding. Although the surface displacements of glaciers can be monitored locally with ground GPS points, this solution is difficult in terms of both implementation and cost. In this paper map of the surface changes on Alam chal mountain glacier of the Alam kuh area (Alborz in North of Iran) is obtained using SPOT5 satellite images as well as aerial photos. In this research required ground control points for DEM production and ortho generation have been extracted from Aerial triangulation of aerial photos in 1:40000 scales taken by National Cartography Center (NCC) of Iran in 2001. The Spot 5 satellite image of the test area acquired in 2004 has been co registered with respect to produced ortho photo mosaic of aerial photographs with an accuracy abut 0.5 pixel size of spot 5. The accuracy of produced Ortho photo have been evaluated using indipenden check points measured by GPS. This study showed that a strong change was occurred during 2001 to 2004 on the glaciers surface. Introduction Accurate displacement measurements are needed to understand the dynamics of glaciers. Such measurements contribute to a better knowledge of the rheological parameters controlling the flow of glaciers. They are important to monitor icefalls, glacier surges (Fischer et al., 2003), and glacier hazards (Ka¨a¨b et al., 2003). They can also detect ice-velocity changes caused by global warming (Rignot et al., 2002). Differential Global Positioning System (DGPS) ground surveys, synthetic aperture radar interferometry (InSAR), and optical image cross-correlation are the main ways to determine glacier displacements. The first two methods are the most accurate but present some severe limitations for the monitoring of mountain glaciers, i.e. all glaciers except large ice caps, ice fields, and the Greenland and Antarctic ice sheets. Today, with the use of differential GPS (DGPS), one can achieve very precise measurement (a few centimetres error), yet limited to a few points in the accessible part of the glaciers. This kind of field campaign is costly and may be difficult. Glaciers might be more or less accessible, and weather conditions might be bad in altitude. Snow might also cover some of the reference points. Aerial or satellite imagery may be used for such displacement measurement. Their main advantage is their spatial coverage, potentially the whole glacier. Satellite radar interferometry has been used for precise ice velocity measurement since 1993 (Goldstein, 1993), and this technique is very adequate for measuring small displacements (up to a few tens of cm), on cloud covered areas. Therefore, this method has proved to be adequate to follow glaciers displacements over a few days. Using repeated visible or near infrared images of the Glacier area can track the displacement of features such as crevasses or surficial debris moving with the ice (Lucchitta & Ferguson, 1986). Development of automatic featuretracking algorithms has substantially increased the accuracy and the efficiency of this approach (Scambos et al., 1992). Furthermore, the measurement is unambiguous: absolute displacements can be referenced to motionless areas which are always available for mountain glaciers. This approach can be applied to images with a large time separation. Some velocity fields have also been derived from optical images separated by more than a year on mountain glaciers (e.g., Ka¨a¨b, 2002). In this paper the changes on glacier surface have been monitored using Aerial photos as well as Spot 5 satellite image. The main objective of this study is to demonstrate that high resolution and surface displacement vectors can be routinely obtained on mountain glaciers using optical satellite and aerial images. Finally results are compared with GPS measurements. Study Area Five main Glacier zones have been identified in Iran as below (Vaziri 2003):
 Fig.1: Map of study Area In Iran the main of water resource for using in urbanism, industries and agriculture are based on natural glaciers, so in the case of water resource management glacier plays important role. Existing Glacier in Iran are mountain Glaciers and because of their volume and extensity, most of them are located in higher mountains (snow line height is near to 4100 m). Therefore, direct study of these areas are time consuming and costly. As a result using satellite and aerial images can be preserved a solution to overcome these problems. Data used in this research: The SPOT5 satellite was launched on 4 May 2002 with a repeat-orbital cycle of 26 days. The ground resolution has been improved with a pixel size of 2.5 m in THR mode, while retaining an area footprint on the ground of 60 km. Precise orbital ephemeris and attitude descriptions are provided with the images. Without any ground control points, an image is located on the ground with a precision of 30 m rms. One scene Spot 5 panchromatic satellite image (2.5 m Resolution) of Alam chal Glacier was acquired in end of September for this research. Six aerial images 1:40000 scales were taken by NCC in October 2001 was also used. GPS measurements (Gathering in field work) and Control points for photogrametric process (absolute orientation) extracted from aerial triangulationare also applied in research. DEM and Ortho photo Generation DEM was product from 1:40000 aerial photos scanned in 14 µm. The required ground control points for photogrametric processing were acquired through a Bundle Block Adjustments Aerial Triangulation. These DEM and ortho photo's the area was produced using VirtozouNT photogrammetric software. Later ortho image mosaic of the whole area was generated (Fig 2). Therefore Spot 5 image registered was co registered with the produced ortho image mosaicwith an accuracy of 0.3 pixel in X direction and 0.4 pixel in Y direction giving an RMSE equal 0.45. In addition, image resampling is carried out with nearest neighbors approach. Fig. 4 presents all the steps required to measure glacier-surface displacement from Spot 5 image and aerial photos.  Fig.2: ortho photo mosaic generation process  Fig.3: Sopt 5 image of Alam chal Glacier  Fig.4: Flowchart of the methodology followed to measure the surface displacements Results After doing the mentioned process, glacier surface changes were detected. These changes may be occurred in two reasons. First, the surface features of the glaciers may change due to melting of snow cover or ice, snowfall or changes caused by windblown snow. Second, good features for the comparison such as the crevasses and the surface big moraines appear from year to year at the same places with similar shapes, change due to suddenly events. For example, the earthquake that accrued in spring 2004 may have made changes in glacier surface.  Fig.5: Comparing Glacier front in ortho photo mosaic with glacier front in Spot 5 image (digit line)  Fig.6: displacement vectors for two moraines Comparing the Spot 5 image with aerial ortho images shows a displacement of 13 m on surface morains during 3 years interval. Using SPOT5 image with a pixel size of 2.5 m, an accuracy abut 0.5 pixel size was achieved. The uncertainties resulted mainly from the difficulty of co registering and removing the topographic distortion between the two images. The resulted images was also evaluated in check point Measured using GPS measurements during Two test field campaigns were planned on Alam chal glacier in August and September 2001. Position of Glacier front, some of surface moraines and crevasse was determined with the GPS. These measurements have a good correlate with ortho photo mosaic (year 2001) that showed precession of ortho photo mosaic (Fig.7).  Fig.8: GPS measurements and ortho photo Conclusion The goal this paper was measuring displacements on Alam chal mountain glacier with SPOT5 image and Aerial photos during 3 years. With visual interpretation and glacier and moraines border digitizing and comparing in two images, 13 m glacier surface displacement was detected. The temporal mismatch between acquisition time of Spot 5 image and aerial photos causes we can't use the automatic algorithms for detection of displacement. Also difference between radiometric and special resolution between these two source data prevent us to using cross correlation automatic algorithms for detection of displacements (Images do not acquired from a similar point of view, and incidence angles). References
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