Mar_Spectra: A UAV-Based Spectroradiometric Platform for Above-Water Environmental Monitoring

Miniaturized optical sensors now allow unmanned aerial vehicles (UAVs) to perform high-resolution monitoring over water surfaces. We present Mar_Spectra, a lightweight UAV-mounted spectroradiometric platform for above-water measurement of ultraviolet and visible reflectance at centimetric spatial resolution. The system was designed as a general airborne sensing platform rather than for one specific target: it combines compact instrumentation, real-time acquisition, and optimized flight protocols for rapid coastal surveys. The payload integrates a miniature UV-VIS spectrometer, an embedded Raspberry Pi controller, GPS, an altimeter, wireless communication, and synchronized RGB imaging, and is suitable for multirotor operation. We developed a full acquisition workflow that covers radiometric calibration, quality control, automated metadata recording, and the tuning of flight altitude, sensor-to-water distance, and acquisition settings to keep measurements stable while limiting rotor-induced surface disturbance. As a proof of concept, we tested the platform for detecting sunscreen-derived ultraviolet filters in coastal waters. Controlled laboratory experiments gave a strong linear relationship between a UV spectral index and UV-filter concentrations measured chemically (R² = 0.964), and successive field campaigns showed that the system resolves spatial gradients of surface contamination under real operating conditions. Wind, suspended sediments, and phytoplankton were the main factors limiting detection. Beyond this case, the modular architecture can take additional optical sensors and address other environmental targets, offering a low-cost approach to UAV-based monitoring of coastal and inland waters.