Abstract
With the ability to capture daily imagery of Earth at very high spatial resolutions, commercial smallsats are emerging as a key resource for the remote sensing community. Planet (Planet Labs, Inc., San Francisco, CA, USA) operates the largest constellation of Earth imaging smallsats, which have been capturing multispectral imagery for consumer use since 2016. Use of these images is growing in the remote sensing community, but the variation in radiometric and geometric quality compared to traditional platforms (i.e., Landsat, MODIS, etc.) means the images are not always ‘analysis ready’ upon download. Neglecting these variations can impact derived products and analyses. Users also must contend with constantly evolving technology, which improves products but can create discrepancies across sensor generations. This communication provides a technical review of Planet’s PlanetScope smallsat data streams and extant literature to provide practical considerations to the remote sensing community for utilizing these images in remote sensing research. Radiometric and geometric issues for researchers to consider are highlighted alongside a review of processing completed by Planet and innovations being developed by the user community to foster the adoption and use of these images for scientific applications.
Highlights
The collection and archiving of Earth observation data has historically been led by government agencies, spurring a range of benefits including continuity in data processing algorithms and more open and public access to the data [1,2]
All PS products undergo some level of geometric correction by Planet, which varies by processing level (Table 2)
Commercial smallsat providers such as Planet are innovating the remote sensing space, which for decades has been controlled by government agencies
Summary
The collection and archiving of Earth observation data has historically been led by government agencies, spurring a range of benefits including continuity in data processing algorithms and more open and public access to the data [1,2]. A shortcoming of the Dove Classic sensors for remote sensing research is the lack of separation in the spectral response for the RGB bands (Figure 2a), making it difficult to use imagery from this oldest generation for precise spectral analyses (e.g., reliable time series of NDVI or Green NDVI). Due to the small PS image swaths (Table 1), mosaicking is often needed and sometimes requires combining multiple sensor generations, especially if a mosaic consisting of images captured on the same day is desired This task is not straightforward given the differences in band placement and channel width across the generations detailed above (Figure 2). Alongside Planet’s coefficients, the remote sensing community has developed regression-based transformation functions so users can adjust the RGB-NIR surface reflectance from first- and second-generation PS sensors to provide more consistent time series. These coefficients are provided by the authors to the user community [10]
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