Ship Based Sun Photometer Measurements
As part of previous Simbios ocean color efforts we employed a hand held
sun photometer to measure aerosol optical depths on ship cruises north
of Oahu, Hawaii (the Hawaii Ocean Time Series, HOTS). Due to the
difficulty of manually pointing a narrow field of view sensor at the
sun on a moving platform we developed a simple approach to reduce (but
not really eliminate) the number of bad misaligned measurements (Porter et al., 2001).
This involved a somewhat subjective method of removing the larger
values which can occur if the photometer is not correctly pointed at
the sun. This approach was later adopted by the NASA SIMBIOS program as
a way to process hand held sun photometer measurements carried out on
ships.
The problem is illustrated in the following figure. On the first day
the ocean was calm and the majority of the hand held sun
photometer measurements form a reasonably tight cluster. On subsequent
days the winds picked up and the ocean grew rougher. As this
occured it became more difficult to point the photometer at the sun and
the number of misaligned values (larger points) increased.