# Integrating Inland and Coastal Water Quality Data for Actionable Knowledge
## 3 Overview of Observational Methods and Platforms
### Remote Sensing
#### 3.3.3 Drone and Aircraft Systems  
The technology for smaller, portable, remotely piloted aircraft systems (RPAS), also known as unmanned aircraft systems (UAS) or, more commonly, drones, has evolved rapidly over the past two decades. These systems consist of both fixed-wing and copter-style aircraft designs, aerial cameras and sensors, navigation systems that include electronics and GPS devices in the aircraft, combined with autopilot devices and/or controllers that communicate with the aircraft using radio frequencies. Current systems utilize cell phones and larger tablet devices with applications enabling a remote pilot to fly using the controller, supported by near real-time images returned from the aircraft's camera. The aircraft can be flown manually or with a flight plan created by the drone manufacturer's software (for example, DJI FlightPlanner), or with specialized applications (for example, Pix4D and Drone Deploy). Typically, hundreds of individual images, captured along gridded flight lines, are mosaicked as a 2-D GeoTIF and brought into raster-based remote sensing software for further analysis and generation of products. Drone capabilities are especially helpful in nearshore and shoreline zones where satellite data suffer from mixed pixel and adjacency effects [86]. Drones can provide high spatial and, potentially, high temporal resolution information and are complementary to satellite and conventional manned airborne imagery platforms. The advantages of drones also include temporal and spatial flexibility, such as reaching inaccessible or dangerous locations [87]. Drones and aircraft can be deployed to fill monitoring gaps (e.g., on cloudy days), albeit at lower spatial extent, and to capture the spatial and temporal variations of water quality parameters within one flight or between flights, which is vital for comprehensive assessments of water bodies [62]. A well-integrated set of recorded tutorials and examples of drone applications for coastal research and monitoring are available from an October 2020 U.S.NOAA-sponsored virtual workshop ([[https://secoora.org/drones-in-the-coastal-zone-workshop/](https://secoora.org/drones-in-the-coastal-zone-workshop/)]([https://secoora.org/drones-in-the-coastal-zone-workshop/](https://secoora.org/drones-in-the-coastal-zone-workshop/)), accessed on July 2021). A variety of conventional cameras and narrow-band imaging sensors (for example, Micasense Altum with RBG, Red Edge, NIR, and Thermal IR bands; Headwall Hyperspec sensors) have been adapted to drones and aircraft, enabling measurements across the solar reflective spectrum, as well as emissive thermal infrared. The following studies have used drones for a variety of water quality measurements: primary production and trophic state [88], harmful algal blooms [89; 90], macrophytes [91; 92], chlorophyll-a [93], total suspended matter (TSM) [94], and turbidity [95]. It is safe to assume that emerging technologies will provide more capabilities in monitoring water quality parameters. Several new drones are designed to be waterproof, enabling water landings and acquisition of shallow submersion underwater photography, or can be modified to collect water samples [96]. As an example, the Saildrone, an unmanned surface vehicle (USV; Saildrone, Inc.) [97; 98] is capable of surfing on the water surface with sensors measuring atmospheric and aquatic parameters. For seawater, ocean currents, chlorophyll-a, colored dissolved organic matter (CDOM), backscatter coefficient, dissolved oxygen, sea surface temperature (SST), and sea surface salinity (SSS) can be measured. The system can be adapted to include other sensors. It is powered by wind and sun and can travel up to an average speed of around 1.25 ms\({}^{-1}\). The Saildrone can perform autonomous long-range data collection (up to a 12-month mission, depending on biofouling). There are numerous commercially-available ASV and small autonomous underwater vehicles (AUV) for water water quality monitoring that are becoming available to all stakeholders.