For every type of measurement, there are tradeoffs in sensor resolution.
Fig. 5 shows some of the most common satellite sensors used for
freshwater ecosystem measurements and their relation in terms of
spectral (x-axis), temporal (y-axis), and spatial resolution (size of the
bubble). HyspIRI's proposed spectral, temporal and spatial characteristics
occupy an observation space shared with only a few other satellite
missions. However, HyspIRI's observational capabilities make it unique
and necessary for freshwater ecosystem measurements, as it occupies
a unique niche in sampling space. Freshwater ecosystemmeasurements
from satellite remote sensing can be classified based on the sampling
strategy and frequency. We categorize these different schemes into
1) continuous samplers, 2) targeted mappers, and 3) global mappers.
Continuous samplers are geostationary satellites that can image high
temporal frequency (e.g., Korea's Ocean Color Satellite GOCI that
makes a measurement once an hour) of a specific location to provide
near-continuous monitoring of dynamic processes such as harmful
algal blooms and river plumes. Continuous samplers provide coarse
spatial resolution over a specific, targeted region. Targeted mappers
can be considered pseudo global mappers. Also in a lower earth orbit
(although not necessarily sun synchronous, e.g., the Hyperspectral Imager
for the Coastal Ocean, HICO, onboard the International Space Station),
targeted mappers acquire data over particular areas based on
data acquisition requests (e.g., NASA's EO-1 Hyperion or commercial
missions suitable for freshwater like Worldview 2 and 3; WV2, WV3),
or regular acquisitions over a region of interest (e.g. the Italian Space
Agency's proposed PRISMA mission, or the German Environmental
Mapping and Analysis Program) thatwill providemapping-like capabilities
over a specific region.