SkyTruth Alerts adds high-resolution planet images to our monitoring toolbox
Norway just gave all of us who love the Earth a tremendous gift: their Ministry of Climate and Environment, through a contract with Planet.com, is providing free access to Planet’s high-resolution commercial satellite imagery for monitoring the world’s tropical forests. The contract advances the mission of Norway’s International Climate and Forests Initiative (NICFI).
Under this new contract, imagery is available free to the public on several platforms, including our own SkyTruth Alerts. Alerts allows users to easily compare scenes across two time periods to identify where changes have occurred, and share those discoveries with others. To accomplish this, Alerts has these features:
- flexibility in creating and managing Areas of Interest (AOIs);
- access to additional sources of satellite imagery for comparison (see discussion below);
- ability to save and share map views;
- options for annotating, and sharing annotated views.
More technically-inclined users can download the data directly from Planet to conduct analyses and create derivative map products. And other platforms, such as Global Forest Watch, also offer this new Planet imagery along with sophisticated tools that allow you to explore global and local datasets covering land use and deforestation in communities around the world.
SkyTruth Alerts provides users unique benefits: This blog post discusses how you can monitor areas of interest using Alerts featuring this new Planet imagery. We are making this imagery available to users on an experimental basis and your feedback is valuable to us. Please give it a try, share this with your friends and colleagues, and let us know what you think!
Satellite Imagery Available on Alerts
While SkyTruth Alerts originated as a vehicle for delivering notifications of environmental incidents from certain government databases, with the addition of satellite imagery it has evolved to become a monitoring tool that more fully embodies SkyTruth’s mission of sharing the view from space to motivate people to protect the environment. The addition of Planet images in tropical countries expands the satellite imagery available in Alerts. Those sources of satellite imagery (as of January 1, 2021) are listed below.
Planet Visual Basemaps
Planet basemaps are composites, or mosaics, of daily images (from PlanetScope) over time, optimized for visual display and interpretation. Visual mosaics offer a true-color (red, green, blue) representation of spatially accurate data with minimized cloud cover, haze, illumination variations, and topographic effects. These are ideal for visually monitoring AOIs inside of Alerts. The spatial resolution (about 5 meters per pixel) is usually adequate for detecting many disturbances on a property, including land clearing, deforestation, and the construction of new roads and buildings (unless they’re hidden below the forest canopy).
Planet basemaps are available in two ways:
- The new imagery available through the NICFI agreement provides semi-annual mosaics for tropical countries from December 2015 through August 2020, and new monthly mosaics starting in September, 2020. The current contract makes this imagery available for at least two years and may be extended to four years.
Planet Surface Reflectance Mosaics (Analysis Ready)
The NICFI contract also provides Surface Reflectance Mosaics that include a fourth band of near-infrared (NIR) data. In these maps, the different shades of red reveal variation in the density, health, and/or type of vegetation. The NIR band makes it easier to see variability in vegetation because the chlorophyll molecule reflects this band very strongly. These maps are useful for detecting and measuring subtle changes in forests that could be caused by disease, invasive species, or thinning rather than intensive clearcutting.
Sentinel-2 is an earth observation mission from the European Space Agency’s Copernicus Programme. Two identical Sentinel-2 satellites operate in tandem to acquire optical (visible and infrared) imagery over land and coastal waters. They capture new images in most areas of the world every five days with scenes available dating back to November, 2015. Because Sentinel-2 scenes come in 290 kilometer (180 mile) swaths, the scenes you select to view in Alerts may or may not fully cover your current map.
Sentinel-2 images can be useful for identifying when changes occur by date. Compared to Planet basemaps, however, Sentinel-2 images have lower resolution (10 meters per pixel) and cloud cover often affects the usability of the images.
Sentinel-1 is another satellite constellation in the Copernicus Programme. The two Sentinel-1 satellites carry synthetic aperture radar instruments that collect images in all weather conditions — day and night — providing new imagery from a few times a week to once every 12 days, depending on latitude.
Sentinel-1 imagery is the main data source used in SkyTruth’s Cerulean and Inambari projects. It can also be used to monitor sea-ice levels and oil spills at sea, and monitor agriculture, forestry practices, and flooding on land. Sentinel-1 images are produced by beaming radar energy down at the Earth and measuring the signal that bounces back up, and look very different from the colorful optical satellite images most of us are used to seeing. So it may take some time for Alerts users to gain an understanding of what’s being viewed with Sentinel-1 imagery.
The Landsat program is a joint effort by NASA and the US Geological Survey. SkyTruth Alerts uses optical images taken by the most recently launched Landsat satellite, Landsat 8, which has been operating since February 2013. These images provide 30-meter spatial resolution every 16 days. Landsat imagery often is used to categorize land use and to document the effects of global warming, urbanization, drought, wildfire, and a host of other natural and human-caused changes. Inside of Alerts, Landsat is useful for quickly scanning large areas at low zoom levels (that is, at less detail), as a first pass to detect signs of activity that could warrant taking a closer look using Sentinel-2 and Planet imagery at higher zoom levels. Each Landsat scene is about 115 miles (185 kilometers) long and 115 miles wide.
Using SkyTruth Alerts to Monitor Areas
Once you have logged into Alerts, you’ll have access to all of the above image datasets by clicking the icon.
To help get you started, we’ve created several maps showing the locations of parks, Indigenous reserves, and other protected areas in selected tropical countries. We downloaded the protected area information from ProtectedPlanet.net (the data include both terrestrial and marine protected areas, although it’s important to note that Planet imagery only extends about 10 kilometers into coastal waters). You can access these maps from Alerts’ Public Maps link at https://alerts.skytruth.org/issues. Our current list includes protected areas from the following countries:
Below is a short video showing how to use these maps and help us monitor protected areas (or other places in the tropics that you care about) for signs of trouble. You can also check out the Alerts How-To Guide for additional instructions on using the application.
If you find something interesting in the satellite imagery or have questions about what you’re seeing, send us an email at firstname.lastname@example.org. Please include a screenshot of your map, or better yet, save your map and include its URL. You might even use the Download Image of Map button and include the JPG image that it creates. SkyTruth is partnering with the conservation group Wildlife Conservation Society to help them detect threats to biodiversity in hotspots around the world. We are also collaborating with staff at the Peruvian parks authority concerned about illegal activities in their protected areas. And so we can pass on any changes you detect to folks working on the ground in these areas who can do something about it.
These are brand new features in Alerts, so we need to hear from you about what works and what doesn’t work! Please try out these features and share your experience with us at email@example.com. And feel free to share this with friends, colleagues, and anyone else you think might be interested in helping us improve Alerts.
Our 2021 roadmap for expanding Alerts includes:
- Conservation Vision: Automatic detection of changes in AOIs and other important locations, with notifications to subscribers.
- Custom Alerts: Users can create their own Alerts notification for the issues and places that matter to them, and send the alert to others.
New development in our Alerts product is driven by users like you, so give it a try and let us know: Which new features do you feel are most important? And what’s missing that could make this even better?