Google_Earth_Engine_JavaScript

This is more of a note to self. I notice that to check my work, I reuse some of the same scripts, and here they are.

Tips for getting started with GEE

Google Earth Engine (GEE) has lots of tutorials that are easy to follow, easy to modify, and easy to get going! I noticed that when I am putting pieces together, or testing bits of code, there are a few tasks I need to do repeatedly. 1. See if my script renders what I think it should in the map pane 2. Looking up what data and data values are available 3. Exporting imagery 4. Finding single images

1. See if my script renders what I want

In the simple example below - I am calling an image to render, it is calling it by it's id and then telling it to render in the map box. Notice, you are not adding any sort of style at all, just loading the data.

Below, you will see that I named the variable elevation because it is calling a dataset related to elevation. Enter the following script into the script pane in GEE:

// Instantiate an image with the Image constructor to call. 

var elevation = ee.Image('USGS/NED');

//this next line is the one you reuse all the time - render the variable you made in the map window
Map.addLayer(elevation);

2. Look up what data and data values are available in the data I am calling

You can print information about the data you are working with into the console pane by adding the following to your script

print('elevation', elevation);

Remember to change the variable to whatever you named your variable. Click on console and information about the one elevation band will be revealed.

3. export imagery

If you simply say print the image, it will print you an ungly grey satellite image, you have to be very specific about what you want to export. In this example, notice I am setting the projection, I am setting the pallette, only loading one band, and stretching it.

// Load a single landsat image 
var landsat = ee.Image('LANDSAT/LC8_L1T_TOA/LC82330512015268LGN00')
  
// Create a geometry representing an export region. Barbados - but this isn't called so don't really need it
var geometry = ee.Geometry.Rectangle([-59.6455, 13.0504, -59.4134, 13.3319]);

// Center on Barbados - but this isn't called so don't really need it again
Map.setCenter(-59.5548, 13.1527, 13); // Barbados

//construct a variable I am visualizing Band 1 which is Coastal - Aerosol	0.43-0.45
var visualization = landsat.visualize({
  bands: ['B1'],
  palette: ['green', 'yellow', 'red'],
  max: .4
});

// This will export the image to my drive, the file name will be yellow.
Export.image.toDrive({
  image: visualization,
  description: 'yellow',
  scale: 30
});

The output looks like this...not very pretty...but hopefully this helps anyway.

You can make movies too! Here is the script just like the example Google provides here, but for Seattle! LandSat 5 images from 1991-2011, showing 12 images per second, and only images with 30% or less cloud cover.

Watch the video

Here is the script to modify and make your own!

// Load a Landsat 5 image collection.
var collection = ee.ImageCollection('LANDSAT/LT05/C01/T1_TOA')
  // Tacoma area.
  .filter(ee.Filter.eq('WRS_PATH', 46))
  .filter(ee.Filter.eq('WRS_ROW', 27))
  // Filter cloudy scenes.
  .filter(ee.Filter.lt('CLOUD_COVER', 30))
  // Get 20 years of imagery.
  .filterDate('1991-01-01','2011-12-30')
  // Need to have 3-band imagery for the video.
  .select(['B4', 'B5', 'B1'])
  // Need to make the data 8-bit.
  .map(function(image) {
    return image.multiply(512).uint8();
  });


// Define the area to export.
var polygon = ee.Geometry.Rectangle([-122.5854, 47.1769, -121.9318, 48.0472]);

// Export (change dimensions or scale if you want higher quality).
Export.video.toDrive({
  collection: collection,
  description: 'SeattleVegetation451',
  dimensions: 720,
  framesPerSecond: 12,
  region: polygon
});

This is so fun!

4. Finding single images

I am sure there is an easier way, but I like using SnapSat when I am dealing with anything LandSat8 related. With this tool you can easily look up individual file names, path and row of an area. I know you can set intersections to find these using GEE, but I just really like this tool.