Overview of PlanetScope Image Quality Improvements
Planet continually invests in the latest hardware and software advancements to improve the PlanetScope image quality. Over the past year, we have pursued a number of enhancements to ensure the clarity, consistency, and reliability of PlanetScope imagery, particularly for customers who are doing time series analysis.
The following document is a high-level summary of these enhancements, and will be continually updated as more are released. For more detailed image quality reports, go here.
Hot Pixel Reductions
Hot pixels are short lines of pixels that are much brighter than the surrounding pixels, and persist from scene to scene in a single band. (They’re the equivalent of a stuck pixel on an LCD or OLED screen.) Hot pixels are often associated with hot columns — lines of slightly brighter than normal pixels that extend from the malfunctioning detector. While hot pixels and hot columns are primarily caused by radiation damage in space, some are present on the ground before launch.
All data PlanetScope acquired after August 2nd, 2021 midnight UTC will be using the new hot pixel and hot column correction algorithm. Archive data back processing before August 2, 2021 has not been done and is currently not planned.
This means that customers will see fewer hot pixels and hot columns in their images. We detect about 98 percent of hot pixels and adjust their brightness to match the surrounding pixels, restoring the integrity of those data points.
SuperDove Visual Sharpening
In June 2021, we released an enhancement that improves the sharpness of PlanetScope visual products (PSScene ortho_visual asset, PSScene3Band visual asset). The sharpening restores sharpness that is lost due to the design of the telescope, resulting in images that are higher contrast and easier to interpret than unprocessed pictures.
The sharpening algorithm is principled, which means it uses a mathematical model of the telescope to predict the correct brightness values. Each band is sharpened separately. Output scenes boost mid-range spatial frequencies (in the range of tens of pixels) to better match the original view of the Earth’s surface. These improvements are only applied to the visual imagery, all other products (i.e. analytic data) remain unaffected by this change.
Band to Band Registration
The SuperDove (PSB.SD) sensor plane consists of eight horizontal stripes that capture eight different spectral bands. To form one image, we use multiple frames to create a composite.
Starting on March 1, 2022 users will see an improvement in band registration for these composites. The band registration per band combination will have less than 0.5 pixels in the 90th percentile. Additional band alignment improvements will be made in 2022. Examples can be found below.
Scene Level Harmonization
Scene level harmonization is a tool within the Orders and Subscriptions API that improves the spectral consistency across Planet’s three generations of Doves (PS2, PS2.SD, and PSB.SD), approximately matching a Sentinel-2 spectral response.
Harmonization is applied for PS2, PS2.SD, and PSB.SD (Dove-C, Dove-R and SuperDove respectively), and allows both sensors to be consistent and compatible with each other. The radiometric values are approximately preserved, but radiometric accuracy is not guaranteed.
With the harmonization tool, customers can now use Dove-C, Dove-R and SuperDoves images together to perform time series analysis. Use of the tool is suggested for customers who desire consistent radiometry between sensors and those using machine learning for training models. It is not recommended for customers who are conducting analysis of water conditions or in northern latitudes.
Read more about our harmonization methodology here.