Using Normalized Differential Vegetation Index (NDVI) Maps

From Wikiagro.com

In this tutorial, you can download a sample dataset with NDVI Maps layers, and review sample applications, including:

• Monitor crop development
• Determine the extent of stressed areas
• Detect patterns due to management practices in a field.
• Ground truthing support, for going to a field to determine the cause of variability detected in an image.
• Directed scouting, can provide guidance in locating specific areas of interest within a field.

Prior to carrying out these exercises, it's recommended to review this article: NDVI Maps

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Contents 1 Download sample data 2 Exercise 01 - Review information related with the NDVI map 2.1 What's in a name? review NDVI images 2.2 Crop History 3 Exercise 02 – Directed sampling based on the NDVI maps 3.1 Create a Field Scouting layer 3.2 Mark field visit locations 3.3 Export Points to the GPS Module 3.4 Upload the Points to your GPS device 4 Exercise 03 – Attach a picture to one of the field visit locations 4.1 Take a picture in the field 4.2 Select the scouting location and attach a picture 4.3 View the picture attached to the scouting location

Download sample data

For these exercises we are going to use  a sample dataset: 'Sample Farm_Remote Sensing'.

To create this project, we can follow these steps:

1. Start GeoAGro GIS 
   
   
2. the first time you Start GeoAgro GIS, the Projects Panel will be empty. Click on the Projects Main Folder, and then on Create, to create a new project
   
   
   
3. Enter as the Poject Name: 'Sample_Farm-Remote_Sensing' -
   ! Please make sure to Check on the option "Retrieve startup data for your project", so you can download the sample dataset
   
   
4. As the initial dataset, select 'Sample_Farm-Remote_Sensing', which can be found under the 'Tutorials_en' folder:  
   
   
5. Accept the next options, and your project should be setup.

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Exercise 01 - Review information related with the NDVI map

The first step is to analyze all the information related with the sample NDVI layers.

What's in a name? review NDVI images

In the references panel, under the Base Map group, you will find Landsat imagery layers, and the processed NDVI layers for each Landsat image.

Double-click on one the NDVI layers that you'll find in the reference panel, to turn it on and zoom to its extents: 'ndvi_LANDSAT_20100701_024_032'

In the name: ndvi_LANDSAT_20100701_024_032:

• ndvi is Normalized Differential Vegetation Index
• LANDSAT, is the satellite system used, in this case images from the Landsat Program
• 20100701 is the date that the image was taken, in format yyyymmdd, where yyyy is the year, mm is the month, and dd is the day.
• 24_032 is the path and row, which indicates what landsat image area was used. For more information on path/row visit the Landsat Program world reference system
  

The NDVI for landsat imagery for 20100701 (Jul. 1st , 2010) is shown.

Click on the plus sign next to the layer name to see the legend. We can see that values range from 0 to 1 (dark green), where the higher NDVI shows more vegetation activity.

Crop History

Crop history can help us to understand the resulting NDVI maps by reviewing the correspondence between NDVI and crop history. See Why is crop history important

1. Please download the crop history for the sample farms from this link , and open the table. 
   
   The layer ndvi_LANDSAT_20100701_024_032 corresponds to  July 7th, 2010; we can see that fields 1,3,4, had Corn planted, and fields 2,5 had Soybeans planted.
   
   
   
   
2. Turn off layer 'ndvi_LANDSAT_20100701_024_032' (see how to turn a layer on/off ) ,
   
   
3. Turn on layer 'ndvi_LANDSAT_20090628_024_032'; this layer corresponds to the crops in June 28th, 2009 , we can see that fields 2,3,4, 5 had Corn planted, and field 1 had Soybeans planted.
   
   

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Exercise 02 – Directed sampling based on the NDVI maps

Create a Field Scouting layer

1. Select the new layer tool to create a new Field Scouting layer. It opens the Layer Creation Wizard.
   
2. Select 'Vector layer' and click on next
   
   
   
3. In the Layer Creation Wizard, enter the following values:
   
   Group: [New Group], in the new group field enter: 'Field Visits'
   Name: Field Visit_Aug2010
   Structure: GPS Points
   
   
   
   
4. Using the Edit Cartography and layer properties  tool , change the appearance of the recently created layer, to points size 10, color purple

Mark field visit locations

In this exercise, you will mark some locations that you´d like to visit based on the  in your farm

1. Make sure the layer 'ndvi_LANDSAT_20100701_024_032'  is visible, to use it as a reference for selecting field visit locations.
   
   
   
2. Make the layer 'Field Visit_Aug2010' Active by clicking on it:
   
   
   
3. Click on the Edit layer objects panel, and select the Add New Object tool.
   
   Enter some sample locations by double clicking on the map area for each point.
   
   
   
4. To assign an identifier to each point in the "Field Visit_Aug2010" layer, first select all objects in the layer by using the Select by rectangle tool
   
5. Then, in the Edit toolbar, go and click on Edit Selected Object's Data tool.
   A data table will open. Complete the “Point” column with correlative numbers; and any other attribute you wish to add.
   
   
   
   

Export Points to the GPS Module

Now we will import the recently created points into the GPS

1. Go to the upper left-hand tab and click on GPS. This will display the window for the GPS Module of Geoagro GIS.
   
   
   
2. Go to the Tools toolbar on the right, and click on the Import from GIS Module button.
   Select the “Field Visit_Aug2010” layer in the dialog box. Click on Accept.
   
   
3. In the next dialog box, associate the Identifier field of the target layer with the Sampling field of the source layer. Click on Accept.
   
   
   
   
4. The points in the “GPS Points” layer have been imported to the map.
   
   

Upload the Points to your GPS device

Please note that you need to work with a GPS model supported by GeoAgro GIS and  make sure that it's properly connected.

 

1. Connect to your GPS: 
   Click on the ‘Connect to GPS Device' button. Automatically, GeoAgro GIS will detect if your GPS device is connected
   
   
   
2. After connecting to the GPS, click on the Upload Objects to GPS Device button. GeoAgro GIS will inform that points are being loaded to your GPS device, as in the figure below
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   Now the georeferenced points with their corresponding identifiers are stored in the GPS device and ready to be set out on site.

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Exercise 03 – Attach a picture to one of the field visit locations

Take a picture in the field

In this exercise we are going to see how to attach a picture taken in the field to a scouting location.

For this purpose, please dowload this sample image to your computer from this link

Select the scouting location and attach a picture

1. Select the scouting location to which we will attach a picture to using the Rectangle selection tool 
   
   
   
   
2. From the Interaction module dropdown, select the Objects file tool
   
   
   The File manager  window will pop-up
   
   
   
3. Click on the Add file button  to browse your computer to select the previously downloaded image
   
   
   The file will be attached or georeferenced to the position
   

View the picture attached to the scouting location

1. To view the recently attached picture, please select the Objects files viewer tool  ,
   from the interaction module
   
   
   
   
2. Select the point with the recently attached file using the Rectangle selection tool 
   
   
   
   
   
3. The Object files viewer will pop-up showing the attached picture
   
   
   
   
4. Clicking on the file name will open the picture in your local PC image viewer