Alerts How-To Guide

View & Compare Satellite Imagery

SkyTruth Alerts offers a couple of ways to view recent satellite imagery for an area you are monitoring. In all cases, your zoom level must be 10 or higher. (We pay a fee to make satellite imagery freely-available to the public. Asking you to create an account and requiring a zoom level of 10 or higher helps us manage the cost.) The FAQ has more information about where the satellite imagery comes from and how it works.

Here are the 3 ways you can view and use satellite imagery:

This option is easy and quick, but does not allow you to select a different date for satellite imagery if the image shown has a lot of cloud cover for the area you are monitoring. SkyTruth Alerts will select the most recent image with less than 25% cloud coverage (for the entire satellite image). The area you are viewing may still have significant cloud cover. If you want to be able to select a date or compare satellite images from two different dates, you will need to create an account.

  1. Move to the area where you want to view satellite imagery. Or search for a place in the search bar.
  2. Zoom in to at least level 10.
  3. Click the Recent Low-Cloud Satellite button. The date of the satellite image appears on the image. If imagery from multiple dates is used, all dates are shown.

This option gives you more control when viewing recent satellite imagery. You can select a different date if your first image has too much cloud cover. You can also compare satellite imagery from two different dates. Once you have logged in:

  1. Move to the area you want to monitor or enter the place you want to monitor in the search bar.
  2. Zoom in to at least level 10.
  3. Click the Satellite Imagery icon on the map toolbar.
  4. Check the Sentinel Satellite Imagery checkbox.
  5. Select an imagery date from the dropdown.
  6. Adjust your cloud cover preferences (optional). The date of the satellite image appears on the image. If imagery from multiple dates is used, all dates are shown.

You can also compare two satellite images from two different dates to see how things have changed on the ground.

This feature requires you to register for an account.

  1. Move to the area you want to monitor or enter the place you want to monitor in the search bar.
  2. Zoom in to at least level 10.
  3. Click the Satellite Imagery icon on the map toolbar.
  4. Check the Sentinel Satellite Imagery checkbox.
  5. Select an imagery date from the dropdown.
  6. Adjust your cloud cover preferences (optional). The date of the satellite image appears on the image. If imagery from multiple dates is used, all dates are shown.
  7. Click “This is my first compare image.”
  8. Select the date from the dropdown that you want to compare to.
  9. Click “This is my second compare image.”
  10. Click the Compare button.
  11. Drag the slider back and forth to see how things have changed over time.

You can mark up and annotate the satellite imagery if you wish, but only the second image, i.e., the right-hand image can be marked up.