Remote sensing lab 4

GSC 512/612 Remote Sensing
Lab Exercise 4 – Multi-date Image Interpretation: Crop Identification

Introduction

In this lab, you will learn to identify agricultural crops and natural vegetation using multi-date multispectral images. The particular datasets were acquired by

Landsat-7 ETM+ and the location was around Murray, KY. The images were collected on the following dates in 2000: April 26, June 13, July 15, September 17, October 19

and November 20. You can find the images on \\Strabo\GSC45\GSC_512_01\Labs\lab4. The names of the images are: etm042600.img, etm061300.img, etm071500.img,

etm091700.img, etm101900.img and etm112000.img. Each image has all 6 reflective bands. Copy the whole lab4 folder to your own directory on D: drive.

Vegetation (natural or cultivated) identification commonly involves multi-date images since many plant species have relatively unique phonological growth cycles.

Landsat-7 ETM+ data have relatively coarse spectral resolution (i.e., using only 6 reflective bands, continuous spectral reflectance curves cannot be achieved). Crop

identification is possible using ETM+ data (or datasets of similar spectral resolution) only if the crops were:
   Planted at slightly different times in the growing season, which caused one canopy to be less developed than the other;
   One crop received significantly different irrigation than the other causing it to produce more or less biomass;
   One crop matured more rapidly than the other;
   The row spacing or field orientation was dramatically different for the two crops;
   One crop has a different canopy structure.

Crop calendars are used to document the unique phonological growth cycles. The graph on the next page shows phonological cycles of a few crops in the San Joaquin and

Imperial Valleys, California, along with Landsat MSS images of three fields during a growing season. (Jensen, 2007).

The following table is a simplified crop calendar for Murray, KY, as seen on the ground. Actual planting and harvesting dates may vary depending on the temperature and

participation in a particular season. You will refer to this table to identify the crops.

Winter (Nov-Feb)   Spring (Mar-May)   Summer (Jun-Sep)   Fall (Oct-Nov)
Winter wheat   Green but dormant   Vigorous growth   Turn yellow in June / harvested   Planted in Oct
Soy beans   Stubble    Single crop planted in May   Single crop – green Double crop – planted after wheat   Harvest early Oct / Stubble
Corn   Stubble    Planted in April/May   Green / brown in late Aug / harvest in Sep   Stubble
Grass/pasture land   Green to brown   Green    Green    Green

In addition to the crops listed in the table, you may also find deciduous and coniferous forest patches in the study area.

Link windows in ERDAS

When multiple datasets of the same area are studied, it is useful to link two Viewer windows, so that you can locate the same spot in different windows. Try this out.

Open etm042600.img in 2D View #1. Add 2D View #2, and load etm061300.img in the second Viewer. Click on the Link Views button in the Home menu, the views are linked.

To verify that, zoom in inside View #1, you will notice a box in View #2 showing the extent of Viewer #1. You can always go back to the full view by selecting Fit to

Frame. Start the Inquire tool, you will notice that the cursors point to the same location in both windows. That makes navigation through the multi-date datasets

easier. You may continue to add more 2D Views and open the images from all dates. You may link as many windows as you would like, but navigating throwing multiple

linked windows may become difficult when three or more windows are linked.

Assignment:

Based on the crop calendar and the multi-date spectral signature of each site, identify the types of crops, grass or forests for the following locations on each image

date. For cropland, also indicate the growing stages (e.g., planted, growing, brown/start to dry, harvested/stubble, and bare ground). Fill in the table. Note: the

sites are marked on a PDF map in the Lab4 folder. You may use the map as a reference to see where they are in addition to their X Y coordinates. You need the images

from more than one date to identify the crops. The same field may go through a crop cycle in a year, for example, winter wheat soy beans, etc.

04/26/2000 06/13/2000 07/15/2000 09/17/2000 10/19/2000 11/20/2000
Site A:
X: 379970
Y: 4051635
Site B:
X: 376749
Y: 4053324
Site C:
X: 375958
Y: 4047809
Site D:
X: 378903
Y: 4056949
Site E:
X: 379350
Y: 4057024
Site F:
X: 381331
Y: 4054650

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