Halifax

Figure 2.1: An infrared image of Halifax, Nova Scotia.

Just to mention again, the source for this image comes from the GeoConnections Discovery Portal website. It is from the Landsat 5 TM Data over Major Canadian Cities geospatial dataset, found at this site. By clicking on the halifax/ file, you will be directed to the Halifax index, where the file halifax_100_ic.zip can be downloaded. When downloaded, the image file, halifax_100_ic.tif can be viewed.

* It should be noted that finding remotely sensed images was difficult at first. Unless a website is known, much time is required to search for the data and downloading also took some time. As well, when the data was downloaded, all the formats were not appropriate for use (i.e., .jpg could not be used because of lost compressed data). However, once downloaded, appropriate files needed to be extracted because their large size had been compressed.

Image Details for Figure 2.1

Data type: image file, .tif format
Source: GeoConnections Discovery Portal, Landsat 5 TM Data over Major Canadian Cities, Government of Canada.
Satellite: Landsat 5
Sensor: Thematic Mapper (TM)
Date of acquisition: September 9, 1989
Geographic location: Halifax, Nova Scotia, Canada
Coordinates: (From the four corners of the image) Datum: NAD 83, Projection: UTM, Zone 20
             Northwest: Northing / Easting 5082925 / 298650
             Northeast: Northing / Easting 5082925 / 548650
             Southwest: Northing / Easting 4857925 / 298650
             Southeast: Northing / Easting 4857925 / 548650
Rows and Columns: 28/29 and 8
Spatial resolution: 25 x 25 metres
Radiometric resolution: 8 bits unsigned per band
Spectral resolution: 3 spectral bands (2, 3, 4)

Source: cd halifax 04.txt file from the halifax/ directory mentioned above, (GeoConnections Discovery Portal 2007). This file provides the metadata for this image.

This image is displayed with the 3 spectral bands 2, 3, and 4 (green, red, and near infrared). They were viewed through the red, green, and blue channels in the order 4, 3, and 2 of the TM sensor. The red in the image depicts vegetation, especially the more intense shades of red. The black portions of the map are water bodies, while the cyan colour around the coast represents sediments dispersed in the water due to tidal action or shallow water levels. The lighter red shades and brown colours represent bare ground and some built up areas while the white also shows built up areas and other human structures.

With the use of the software, PCI Geomatics, this Halifax image can be modified. For example, a simple change would be to zoom in on a specific location within the image. Figure 2.2 displays such an action.

Figure 2.2: A zoomed viewed for a section of the original image.

By using this feature, more details of a local area can be viewed. This could be extremely important if a problem needs to solved for a smaller scaled area. Therefore, although this image was taken above the Earth's atmosphere, a detailed image can be produced to aide with solving a site specific problem. For example, looking at Figure 2.2, more details for the water bodies can be viewed.

Another adjustment that can be made to a remotely sensed image is to enhance it. This action helps to improve "the visual appearance" of the image (Campbell 2002) and is displayed with Figure 2.3.

Figure 2.3: A linear enhancement of an infrared image of Halifax, Nova Scotia.

There is a clear difference between Figure 2.2 and 2.3 in terms of colour. This is because of the enhancement used, which was a linear strech, a type of contrast enhancement. This type of transformation increases the number of values for brightness ranges (Campbell 2002). By increasing the number of range values, the image will have a better contrast and show more details. More specifically, a linear stretch produces a new range of values by increasing and decreasing the maximum and minimum values, with all values in between also adjusting appropriately (Campbell 2002). For example, Figure 2.3 provides a better view of the built up area in the lower left portion of the image, compared to Figure 2.2.

For more differences between these images, click here to view some statistics.

As well, if you are interested in remote sensing and would look some questions answered, visit the following links:
            Environmental Photographic Interpretation Center of the U.S. Environmental Protection Agency
            NEODC tutorial and self-help pages. NERC Earth Observation Data Centre (NEODC) is part of the Natural Environment Research Council (NERC) and its goal is obtain, store and provide remotely sensed data of the Earth (NERC Earth Observation Data Centre 2007).

(Images for this page are from my F drive, under the folders, GEOG 4440 3.0 Assignment 0, and Halifax.)