# Tracking Dynamic Northern Surface Water Changes with High-Frequency Planet CubeSat Imagery
###### Abstract
Spring river ice breakup and associated peak flow and flooding can lead to rapid changes in surface water extent [15; 16]. Such peak flow events are critical for recharging lakes and wetlands, transporting water through low-relief floodplains [8; 17; 18]. Warming Arctic temperatures have increased interest in understanding how surface water extent responds to thawing permafrost [19; 20]. Permafrost acts as a barrier between the surface hydrologic system and the groundwater system, meaning that in discontinuous permafrost, the surface water and groundwater systems are connected where permafrost is absent but disconnected where permafrost is present [19; 21]. In high latitude wetlands underlain by discontinuous permafrost, such as the Yukon Flats in central Alaska, decadal-scale analyses (>30 years) of interannual patterns in lake area have noted variable changes in surface water extent due to a combination of thawing permafrost, shortening spring duration of snow cover, changing water balance and underlying hydrogeology [22; 23; 24; 25; 26]. Despite evidence that sub-seasonal cycles strongly influence patterns in surface water extent, potentially obscuring climate-related trends [23], little research has focused on fine-scale, sub-seasonal variability in these areas, due to the absence of sufficient high resolution, high frequency imagery. Recent development of small, affordable satellites known as CubeSats opens new possibilities for studying fine-scale, temporally dynamic hydrological processes from space. CubeSats are typically about the size of a bread box (0.003 m\({}^{3}\)), and contain little more than a four-band multispectral camera and power/downlinking equipment. Owing to their small size and low cost, CubeSat imagers can overcome the tradeoff between high spatial and high temporal resolution by deploying them in a multi-satellite constellation. This approach relies on both satellite mass production and declining launch costs, making CubeSats comparatively affordable for commercial satellite companies to launch and operate [27]. A notable example is Planet (formally known as Planet Labs; [[http://planet.com](http://planet.com)]([http://planet.com](http://planet.com))), a company that has successfully built and launched 281 CubeSats since 2013. With 148 CubeSats in sun-synchronous orbit, Planet currently images nearly all of the global land surface at 3-5 m resolution daily, providing near-real time imagery to paid and academic subscribers. This large volume of frequent, high resolution imagery holds potential value for hydrological applications because open water surfaces are among the simplest land covers to discriminate in visible/NIR imagery, and frequent observations are necessary to track dynamic hydrologic processes such as flood waves and river ice breakup. However, CubeSat imagery is acquired using inexpensive sensors which cannot achieve the same radiometric quality, consistency and signal-to-noise ratios of space agency-funded missions [28]. Together with the newness of CubeSats, prevailing concerns about cross-sensor calibration, image quality, geolocation accuracy, and data availability have limited the advent of CubeSat-based hydrological research. Despite the strong potential of frequent, high-resolution CubeSat imagery to transform hydrological remote sensing, such data remain generally untested and unproven within the hydrologic community [27]. Here, we present a first demonstration of the use of CubeSat imagery to track sub-seasonal changes in surface water extent.