Lab 4:

Accessing, Displaying and Working

with Raster Data Products

• In ArcGIS, images are treated as raster data models.

• They consist of cells (pixels) aligned in horizontal rows and

vertical columns.

• Each cell contains a value that represents reflectance

(intensity, brightness) of the cell’s feature(s) within a defined

spectral range (i.e., wavelength). The reflectance is expressed

on the scale defined by the image’s radiometric resolution (8

bit, 11 bit, …).

• Reflectance can be recorded in

many parts of the electromagnetic

spectrum, however to view such

images with the human eye, the

reflectance levels are shown as

black-and-white for a single band

or as an R,G,B (red, green, blue)

colour composite.

Images in GIS

The symbology tab of the layer properties for a raster image. .

.

Image Symbology in GIS

Images can be shown

as black+white

(single-band) or as an

RGB composite

Individual bands can

be turned on or off, or

the band combinations

can be changed

Contrast stretches can

be applied to better

distinguish features in

the imagery

Landsat-8 OLI and TIRS Image Bands.

Image Band Combinations

Landsat-5 TM Image Bands

Bands Wavelength (micrometers)

Resolution (meters)

Band 1 - Coastal aerosol 0.43 - 0.45 30

Band 2 - Blue 0.45 - 0.51 30

Band 3 - Green 0.53 - 0.59 30

Band 4 - Red 0.64 - 0.67 30

Band 5 - Near Infrared (NIR) 0.85 - 0.88 30

Band 6 - SWIR 1 1.57 - 1.65 30

Band 7 - SWIR 2 2.11 - 2.29 30

Band 8 - Panchromatic 0.50 - 0.68 15

Band 9 - Cirrus 1.36 - 1.38 30

Band 10 - Thermal Infrared (TIRS) 1 10.60 - 11.19 100 * (30)

Band 11 - Thermal Infrared (TIRS) 2 11.50 - 12.51 100 * (30)

Bands Wavelength (micrometers)

Resolution (meters)

Band 1 – Blue 0.45-0.52 30

Band 2 – Green 0.52-0.60 30

Band 3 – Red 0.63-0.69 30

Band 4 – Near Infrared (NIR) 0.76-0.90 30

Band 5 – SWIR 1 1.55-1.75 30

Band 6 – Thermal Infrared 10.40-12.50 120* (30)

Band 7 – SWIR 2 2.08-2.35 30

* Originally

collected at

coarser

resolution,

resampled for

product

distribution

True-Colour Display Red Reflectance shown as red

Green reflectance shown as green

Blue reflectance shown as blue

Colour-Infrared Display NIR Reflectance shown as red

Red reflectance shown as green

Green reflectance shown as blue

Natural-like Display SWIR Reflectance shown as red

NIR reflectance shown as green

Red or Green reflectance shown as blue

Common Band Combinations:

Image Symbology in GIS

Example contrast stretches in ArcGIS. . .

Image Symbology in GIS

No Stretch 2 Standard Dev. Stretch 1 Standard Dev. Stretch

Percent (Tail) Clip Stretch Histogram Equalization ‘Stretch’

None Linear

Root Adaptive

Equalize Infrequency

Example contrast stretches.

Image Symbology in GIS

In this Lab exercise…

• You will need to know how to find, access, and

display raster datasets using:

– USGS Earth Explorer

– GeoGratis

– CSF Net (EOSD) Data Extraction Tool

• You will be working with the following types of

raster data:

– LANDSAT satellite imagery

– Digital Elevation Model (DEM)

– Land Cover Classification

LANDSAT 8 Satellite Image

EOSD -Land Cover Classification Earth Observation for Sustainable Development of Forests Project

• Developed principally by the Canadian Forest Service and Canadian Centre

for Remote Sensing

• Objective - produce a consistent, national-level forest classification product

by way of classifying remotely sensed imagery

Digital Elevation Model (DEM) As with any basic raster layer, where every cell has a value, a DEM is a

“single-layer” raster product where the value for each cell should be the

elevation at that location. DEM’s are produced at a variety of scales and

spatial resolutions.

Using the USGS Earth Explorer to Download Satellite Imagery

You will need to be registered to download most types of data. You can register by clicking on the link here:

Use the Search Criteria tab to locate a desired location. Once you select the location, it will be marked on the map.

Using the USGS Earth Explorer (2)

If you are looking for imagery for a certain date or a specific season, you can specify those parameters under the Date Range tab.

You can also use the map extent to define the area you want imagery for. Simply zoom in on your desired area and click Use Map.

If you want to outline a more specific area, you can click and drag each coordinate outlining the area.

Once you have specified each of the parameters, click Data Sets to see what is available for download.

Using the USGS Earth Explorer (3) A series of data set options will appear on the left. Click on the plus symbol to see the data under each category. Check off the box for the data that you desire (e.g., Landsat 8 Imagery (L8)). You can select more than one data set, if needed,

Once you have specified each of the parameters, click Results to see what is available.

Landsat 8 Imagery (L8) is available in multiple formats. Level-1 products have had geometric and terrain corrections applied, along with a basic radiometric correction. Level-2 products have been additionally corrected to surface reflectance, accounting for atmospheric conditions at the time of acquisition.

Using the USGS Earth Explorer (3) This dropdown box will allow you to switch between the search results within different data sets (if you selected more than one)

When you decide which of the data you want to download, click the download button.

The data products that fit your search criteria are displayed here.

When you click the footprint button, the extent of the satellite photo is displayed on the map (e.g., the green and purple)

Using the USGS Earth Explorer (4)

After you click download, a new window will pop up with several options. Select the Level 1 GeoTiff Data Product

The data will be downloaded in a compressed zip folder.

Using Geospatial Data Extraction to Download a Digital Elevation Model (DEM)

Use the Data Extraction Tool

Use the Location tab to search for a particular area or NTS Mapsheet number

Searching for the specific area that you want (e.g., Thunder Bay) or an area close to your desired location will assist you in narrowing down the extent of the Clipping Area for the DEM.

1. The current map extent (the view of the map on the right)

2. A pre-defined area (e.g., an NTS Map Tile)

3. A custom area outlined by coordinates or a shape drawn on the map on the right

Use the Select Clipping Area tab to define the extent of the DEM you would like to download

The extent of the data can be defined by:

Scroll down to define the projection and resolution for the DEM data

Use the Select Data Options tab to define the type of data you want to download

Specify that you would like the DEM product in a GeoTiff format.

Fill in your email and click the submit button. Shortly after you will be notified when the data is ready.

Use the Submit Request tab to place an order for data to be processed and sent to your email