Tuesday, April 29, 2008

GIS and Satellite Remote Sensing for Arachaeology

Satellite remote sensing can provide a variety of useful data for this type of research. A variety of sources for such data exist, and while the data can be expensive and require extensive digital image processing, they provide a synoptic view which is not available from aerial photography. It takes over 200 aerial mapping photos to cover the same area as a single satellite image. We have used a variety of satellite data for this project, including older Landsat MSS from the late 1970's and more modern French SPOT and Radarsat data. New systems with 1 meter spatial resolution are now commercially available, but have not been used in this project due to cost (donations are welcome!).

The image at right is a SPOT image overlaid on a digital elevation model of the area.

Landsat Multi Spectral Scanner (MSS)

Early in the project the only available remote sensing data was Landsat MSS, with 80 meter spatial resolution. Two images were acquired and digital image processing was conducted to generate color composite images and vegetation maps.

The following images are from the 22 March, 1973 image of the region shown in false color infrared.

This first image shows the entire study area, with the pasture lands shown in pink, forest in darker reds, urban in gray, and water in black.

The image at right show the northern part of the study area. Al left you see the southern part of the research area. The banding is an artifiact of the data, and was later removed using digital image processing techniques. You can clearly see the river and gravel mines along it.

French SPOT Data

The commercial civil remote sensing system developed by the French is called SPOT. It has a spatial resolution of 20 meters for multi-spectral data, which records information in three bands of the spectrum, and a 10 meter spatial resolution for a panchromatic band. The resolution of these images available from space can provide significant improvements in the utility of these data for regional archaeological and environmental applications, especially (as in France) where the field size is very small. Accurate modern landcover maps can be produced using SPOT satellite imagery. Below is a SPOT image which has been classified into a landuse/landcover map of the area. Yellows are pasture, greens are forest, blues are water, and reds are urban. This image was then combined with a shaded relief map (derived from a Digital Elevation Model) to produce a realistic representation of the landscape.

This is a SPOT land use/landcover image draped over the Digital Elevation Model from the project GIS database. Click on the image to see the larger version. You can clearly see the river valley down the center of the image, and the Morvan mountains at the top. The confluence of the Arroux and the Loire is at the bottom of the image. The red line at bottom is the modern highway from the town of Digoin at the confluence of the rivers, and Paray-le-Monial at right. The larger blue areas along the river are the lakes that the gravel mines leave after they remove the materials.

This is a color infrared SPOT 20 meter image, acquired 9 Nov. 1986, showing Mt. Beuvray, site of the ancient city of Bibracte, at upper left. The Arroux river valley flows from top to bottom on the right side. The city of Autun, ancient Augustodunum Aedorum, is at top right.

A close-up view of Mt. Beuvray, 9 Nov. 1986.

SPOT Satellite landcover map-modern vegetation

RADARSAT imagery

Canadian RADARSAT-1 satellite imagery has been acquired of the region on 4 November, 1998 with a spatial resolution of 8 meters. This system is different from SPOT or Landsat in that it is an active radar system that sends its own burst of electromagnetic radiation down to the ground which is then bounced off the surface and recorded on the satellite. Analysis of the Radarsat is ongoing. This system can operate day or night and through cloud cover. It provides a different and new way of visualizing the area. This image is C band, HH, descending orbit, right look, FINE mode. Inc. angle 39-42 degrees.