Presenter: Moritz Lehmann (Xerra)

Description:
Satellite-borne hyperspectral imagers detect spectral nuances in the reflected radiometric signal beyond the capability of multispectral optical sensors. These measurements promise the large-scale monitoring of detailed phenology of Earth’s surface biotoa, for example, the species succession of aquatic algae, or forest biomass and health. The enhanced spectral detail of the data requires hyperspectral in situ measurements to support calibration, validation, and the development of suitable atmospheric correction methods.  We report in situ hyperspectral and ancillary measurements obtained over three years in a group of lakes that we consider a natural lab for remote sensing studies. The complex of volcanically-formed lakes known collectively as the Te Arawa or Rotorua Lakes in the North Island of New Zealand are morphologically diverse and range from oligotrophic to eutrophic. In addition to long-term monthly water quality monitoring data from eleven lakes, five lakes are instrumented with autonomous monitoring buoys. Fitting inside a box of 35 by 35 km, the entire area is often imaged in a single swath by Earth observation satellites and many lakes are large enough to fit a 1-km square water-only pixel. Our bio-optical measurement suite includes chlorophyll a, suspended particulate matter, coloured dissolved organic matter, phytoplankton cell counts and particulate absorption. We characterised seasonal and episodic bloom conditions by their hyperspectral reflectance signals and tested spectral algorithms for suitability for future monitoring applications. In addition, data from an overpass of the Italian hyperspectral satellite (PRISMA) is contrasted to in situ spectra and expected distributions of chlorophyll a. Our plans for the future include expansion of the instrumentation of the monitoring buoys to include hyperspectral reflectance sensors to contribute fiducial reference measurements for current and upcoming satellite water colour instruments.