Challenges to autonomous sampling—Sampling by autonomous
platforms that operate over long periods, such as
Washington coast Seagliders or biogeochemical ARGO
(Array for Real-time Geostrophic Oceanography) floats
(cf. Boss et al. 2008 and Martz et al., 2008), present
challenges for collection of high-quality data. Major
challenges for gliders include sensor validation and data
interpretation, in part a consequence of restricted battery
energy. Sensors can drift or foul, sensor configuration or
location on the platform may not always be optimal,
collection of water samples to validate actual concentrations
is usually not possible for completely autonomous
missions, and comparison of data from different optical
sensors can be problematic for several reasons. In our case,
Seagliders have been operating in Washington coastal
waters nearly continuously for more than 4 yr, with a single
deployment typically lasting 5–6 months. Sensors do not
appear fouled even after the longest missions, most likely
because Seaglider spends a small fraction of its time in
biologically rich, near-surface waters and temperatures are
relatively low even in near-surface waters.