ReCON: Regional Coastal Oceanography with Nanosatellites

Earth remote sensing typically involves traditionally-launched and maintained satellites (launched and maintained by government agencies such as NASA, NOAA, ESA, JAXA, etc.). These satellites, such as NASA’s MODerate Resolution Imaging Spectroradiometer (MODIS), NOAA’s Visible Infrared Imaging Radiometer Suite (VIIRS), and the Sentinel-3 Ocean and Land Colour Instrument (OLCI), provide multi-spectral band sets with daily repeat coverage at fairly coarse spatial resolution (> 300m). Use of these sensors presents challenges in complex coastal waters where proximity to land introduces additional spectral complexity in the critical optical properties key to water color (e.g. suspended sediments, bottom reflection, and colored dissolved organic matter). Furthermore, the coarse resolution can result in significant data loss when land pixels are nearby (e.g. anything within 3km from the coast for a 1 km resolution sensor would likely be treated as a land pixel or suffer from land contamination and need to be removed). Rivers and estuaries suffer from the same effect and are not usually available. Critical areas such as these are unable to be monitored with sensors such as MODIS, VIIRS, and OLCI.

Increasing involvement by commercial entities, including satellite development, launch, and operations, is now becoming more common. These organizations are now deploying low-cost nanosatellites with high resolution. Planet (previously known as Planet Labs) has over 175 of these “Dove” orbiting nanosatellites (known collectively as PlanetScope, weigh 4-5 kg) that are currently providing high temporal (daily) monitoring of the Earth’s landmass and most coastal areas at a resolution previously available only by unreliable, high-cost tasking of a few satellites (such as WorldView 3 and 4). These high resolution (3.125m ground resolution) Dove nanosatellites are multispectral, with blue (485 nm), green (545 nm), red (630 nm) and near-infrared (820 nm) bands. Planet has an additional five-satellite constellation called RapidEye, operational since 2009 with a ground resolution of 6.5m. The RapidEye constellation’s band set is not quite as broad as PlanetScope’s and also consists of slightly different wavelengths (blue: 475 nm; green: 555 nm; red: 657 nm; near-infrared: 805 nm). RapidEye minisatellites (weigh 150 kg) have an additional “red-edge” band that will aid in atmospheric correction, centered at 710nm. Both PlanetScope nanosatellites and RapidEye satellites have been radiometrically cross-calibrated to correct for any inter-sensor artifacts and provide top of the atmosphere radiances, and PlanetScope nanosatellites provide daily repeat coverage. Global coverage daily at this resolution has never been achieved until now and we at the Naval Research Laboratory (NRL) are starting a 3 year project to work with this technology.

The overarching goal for the Regional Coastal Oceanography with Nanosatellites (ReCON) project is to utilize the potential for high-resolution nanosatellites to monitor coastal, estuarine, riverine, and other maritime environments in support of U.S. Navy operations. Specifically, during the course of this project (begins October 2018 and ends September 2021) we will develop suitable atmospheric correction, calibration, and optical inversion algorithm methods that will allow us to utilize the emerging and rapidly growing nano-, micro-, and mini-satellite technologies. Furthermore, we will examine the use of the nanosatellites to locate and track, in real-time, river, estuarine, and coastal objects and hazards, inundation, and identify fine-scale ocean features. The extraordinarily high spatial and temporal resolution inherent to nanosatellite data streams provides an opportunity to monitor the environment in ways previously impossible with traditional satellite platforms. However, very high resolution yet highly distributed data sources present many research challenges that must be overcome in order to fully exploit these inchoate satellite technologies.

We at NRL within the Bio-Optical Physical Processes and Remote Sensing Section have vast experience in processing, analyzing, and developing algorithms for ocean color bio-optical properties from a variety of sensors that are viable in complex coastal waters. Specifically, our section has demonstrated this experience over the last twenty years with the continued development of the Automated Processing System (APS). APS is used to ingest multi- and hyper-spectral remote sensing data from continuously imaging ocean color sensors to automatically produce numerous products of interest to Navy operations and inputs to bio-optical forecasting models. These Navy support products are derived from optical properties, including but not limited to vertical and horizontal visibility products produced from Apparent Optical Properties (AOPs) and Inherent Optical Properties (IOPs) and Electro Optical (EO) system performance products for cameras, lasers, and divers. We are well suited for establishing and evaluating new atmospheric correction techniques with limited band sets such as PlanetScope and RapidEye technologies, vicarious and inter-sensor calibration routines, developing and applying sensor specific spectral/bio-optical algorithms, monitoring coastal change and inundation, detecting and tracking objects, and detecting fine-scale ocean features and navigation hazards.