We all have a favorite place we hope will never change. A hometown or vacation spot maybe. But over time, places do change. Sometimes due to economic conditions. Sometimes due to environmental shifts. Temporal resolution helps us see these changes from space.
While spatial resolution refers to the distance between pixels in an image, and spectral resolution quantifies the content of each pixel, temporal resolution is how often a pixel is collected. It enables us to track both natural and human-caused changes to our planet over a period of time. Kind of like a time machine.
The past, present, and future of temporal resolution
Temporal resolution draws on past collections, which archive an individual satellite’s lifespan of imagery or a compilation of images from an entire constellation of satellites, to establish a historical foundation. Then, current collections provide new imagery to build on that foundation, enriching the temporal resolution.
Dictated by demand and limited by capacity, current collections focus on areas of high demand. However, as more companies launch satellites and technology advances, we will be able to broaden collection coverage and increase frequency. And we’re talking the not-too-far-off future. Space is pretty popular these days.
A collaborative effort
Since major changes are progressive, we don’t need to collect every inch of the planet every day. DigitalGlobe has five active satellites in a sun-synchronous low-earth orbit. They’re about 400 miles above the Earth’s surface circling the poles every 90 minutes at 15,000 miles per hour. This allows the satellites to collect images between 10:30am and 1:00pm, leveraging the sun as a flash to minimize shadows.
DigitalGlobe complements its constellation with low- and mid-resolution satellites, like USGS Landsat, which orbits in continuous-collect mode providing near-complete coverage of the Earth’s surface every seven to eight days, to detect change on a global level. Lower resolutions capture about 15 m per pixel, providing the big picture. Once a change is detected, DigitalGlobe can task its high-resolution satellite to zoom in using 30 cm imagery (spatial resolution) to really investigate that change.
This approach using temporal and spatial resolutions is critical in monitoring environmental changes, such as deforestation, coastline shifts, and impact of construction. For example, temporal resolution aids in detecting a change in large forest areas. High spatial resolution allows us to zoom in to identify possible factors causing the deforestation, such as human activity, wildfires, drought, or tree disease.
DigitalGlobe captured Tesla’s Gigafactory in Nevada over a three-year period. Here you can see signs of groundbreaking for construction — land is being cleared, a presence of trailers, etc.
In this image, you can see more progress of the construction. Temporal resolution imagery provides a foundation to help predict what’s happening, monitor progress, and detect change.
High temporal resolution delivers subsequent collection over time to validate predictions, study changes, and provide evidence for legal disputes or compliance. And as we move forward, future collection capacity will allow us to capture and understand even more about our changing planet.