GIS 4035: Module 8 - Thermal Imagery

This week's lab involved manipulating multispectral imagery and using bands in the thermal infrared range to do remote sensing work. While the map below does not display imagery in the thermal infrared (Band 6 in imagery provided by the Enhanced Thematic Mapper Plus suite of satellites), it was used as part of the map analysis performed this week. The map identifies a field network of rice paddies near Guayaquil, Ecuador. Their appearance is somewhat anomalous in the Near Infrared. Healthy vegetation tends to be highly reflective and appear bright in Near Infrared bands (bands 4, 5 and 7 in ETM+), but these fields are dark in those ranges, while appearing like normal, green fields in natural color (where the visible red, green and blue bands are displayed as red, green and blue). In the Thermal Infrared, where captured EMR tends to be the result of heat emissivity rather than reflected, these fields were also intensely dark. During the day (when these images were recorded), water tends to be the coolest material recorded. Vegetation is usually cool, too, but is still somewhat warmer than water. The field'd Thermal IR appearance matched nearby water bodies closely and were darker than areas of healthy vegetation. The inference made was that these were rice paddies - flooded fields planted with rice seedlings. In the NIR and TIR, this gave the fields the appearance of being water, but the seedlings managed to show the signs of photosynthesis to the visible bands (absorbing blue and red, reflecting green to some degree). The latter is probably due to the shallowness of the water.

Rice Paddies in Guayaquil, Ecuador (shown in 'natural' false color)

GIS 4035: Module 7 - Image Preprocessing 2: Spectral Enhancement and Band Indices

This week continued the work with Erdas Imagine and satellite imagery, beginning a deeper delve. Imagery from Landsat 5 Thematic Mapper was provided with the six bands that maintain the same spatial resolution included (Blue, Green, Red, Near Infaread and two mid-level Infrared bands). Several exercises provided practice manipulating and interrogating the images, combining various bands so as to make various features stand out. For example, the most common false color combination where the display layers for Red, Green and Blue are re-mapped respectively to Near IR, Red and Green was given a good workout.

The deliverables this week were created as part of a treasure hunt. The features were described spectrally and had to be located somewhere in the study area of the imagery. Feature 1 represented typical water features, which tend to absorb most electromagnetic radiation in the near infrared band. Feature 2 turned out to be snow, ice and glaciers, which appear bright (high radiometric values) in bands 1-4, but quite dark in bands 5 and 6. Feature 3 was an unusual water feature that had radiometric gradations in 1 - 4 and was somewhat brighter than other water features in these bands. Each feature was displayed in a map with a different combination of bands being used along the RGB display bands.

Feature 1: A Lake

Feature 2: Ice & Snow

Feature 3: Another Lake, with radiometric gradations

GIS 4035: Module 6 - "Spatial Enhancement"

This week continued our introduction to Erdas Imagine with some practice using image filters on raster imagery. This included running various high and low pass filters on an image, as well as edge enhancing and other filters. The map below was produced as an attempt to rectify data errors produced on images from Landsat 7, which sometimes produces bands across an image without any data. A fourier transform was used to reduce the banding somewhat, and then a sharpening filter was run on the resulting image in order to improve the image resolution. The results were not great, but the banding was somewhat reduced compared to the original image.

Moderately corrected banding of Landsat 7 image