Chesapeake Bay Remote Sensing Program Data

The Chesapeake Bay Remote Sensing Program (CBRSP) has used measurements of
ocean color from light aircraft to estimate chlorophyll concentrations in
Chesapeake Bay for the past thirteen years. Chlorophyll is a photosynthetic
pigment common to microscopic algae - phytoplankton - the main primary
producers that comprise the base of the food web in the Bay. This important
pigment imparts color to the water. Clear blue water has low chlorophyll and
reflects strongly at low wavelengths in the visible spectrum, whereas green
water has higher chlorophyll and absorbs strongly in the blue, reflecting light
at longer wavelengths. Data are collected using airborne radiometric
instruments that allow us to measure the reflected light and ascertain
concentrations of chlorophyll. This key property is one of the main ingredients
we need to estimate primary productivity and to gauge the overall productivity
of the ecosystem at higher trophic levels.

The 1989-1995 data were generated using the Ocean Data Acquisition System
(ODAS), a relatively simple ocean color instrument that was developed in the
mid-1980s at NASA Goddard Space Flight Center. ODAS consisted of three
radiometers in the blue-green region of the visible spectrum that measured
water-leaving radiance at 460, 490 and 520 nm. 1995-96 data were generated by
the SeaWiFS Aircraft Simulator (SAS II) that replaced the ODAS instrument. SAS
II contained sensors at seven wavebands, including the six visible bands of the
SeaWiFS satellite ocean color instrument. The additional bands of SAS II
allowed improved recoveries of chlorophyll in highly turbid conditions and at
the extremely high concentrations that accompany red tides. A new version of
the SeaWiFS Aircraft Simulator (SAS III) went into service in 1997 and we
continue to use this instrument in Bay and tributary flights at this writing.
SAS III is a 13-band instrument with improved spectral resolution. All the
instruments (ODAS, SAS II, SAS III) are paired with an infrared temperature
sensor that we use to measure sea surface temperature during flights. One of
our principal sponsors, the NOAA Chesapeake Bay Office, has been the main
distributor of imagery derived from the flights in a continuing collaboration.

In addition to the weekly surveys of main stem of the Bay, CBRSP has conducted
monthly tributary surveys of the Choptank and Patuxent Rivers since 1999. The
Choptank and Patuxent River flights began as a part of the Coastal Intensive
Site Network (CISNet), a goal of which was to measure chlorophyll in two
systems with strongly contrasting watersheds, agriculture in the case of the
Choptank, suburban in the case of the Patuxent.