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13 November 2007: Prepared for OCB data system by Nancy Copley (Biology Dept, WHOI)
and Cyndy Chandler, BCO-DMO (MCG Dept, WHOI).
Methodology
It is important to note that two different light-profiling systems were used
for the EDDIES experiment. The Weatherbird II used a Satlantic profiling
radiometer system (SPMR/SMSR), which has been a standard operating procedure
for BBOP over the past 8 years. The Oceanus used a Satlantic Micro-Profiler II.
R/V Weatherbird II
Satlantic Light-Profiler Description
SPMR
The profiler used aboard the Weatherbird II is a SeaWiFS Profiling Multi-
Channel Radiometer (SPMR). It is a free-falling instrument that is equipped
with two sensors, collecting the upwelling irradiance (Ed) and downwelling (Lu)
radiance at the following 11 wavelengths: 324, 340, 380, 412, 443, 490, 510,
555, 565, 665, and 683nm. The unit is protected in a long case that contains
the majority of the system's electronics, while the optical sensors are located
at either end of the case and face in opposite directions (i.e., up and down).
These sensors measure the irradiance in units of uW/cm2/nm and the radiance in
units of uW/cm2/nm/sr. Tilt and pressure are recorded at the same frequency as
the irradiance measurements (6Hz).
SMSR
The SPMR is accompanied by a deck reference sensor, called the SeaWiFS
Multichannel Surface Reference (SMSR). This sensor is equipped with the same 11
wavelengths as the SPMR, and is based on the same electronics. Data acquisition
is synchronized between the SPMR and the SMSR and is performed at the same
(6Hz) frequency.
CALIBRATION
The system is calibrated with respect to NIST standards three times
a year at UCSB and variation from those standards has been less than 2%.
However, most of this variation has occurred within the UV and blue channels
(as opposed to the red) and is partly due to the lower output of calibration
lamps at lower wavelengths. All other changes in sensitivity were most likely
due to the replacement of the sensors' cosine collectors.
DATA COLLECTION
An SPMR profile begins after the instrument has been deployed
and reaches a distance of approximately 50 meters from the ship's stern (to
avoid ship shadow). The instrument is then released and falls at approximately
0.5 m/s and is synchronized with the SMSR on the deck of the ship.
DATA PROCESSING
The Weatherbird radiometric data were processed using a series of
standardized BBOP processing scripts written by research members at ICESS.
This system creates a quality controlled and quality assessed 1m binned data
set. The irradiance values at "just below the surface" or "(0-)" are obtained
as the intercept of a least squares regression fit of each profile. The
calculated intercept is a product of the diffuse attenuation coefficient (Kd)
calculation. As a result, if the optical properties are propagated to the
surface, the Kd profile for each optical variable (Ed, Lu) will be calculated
as well.
i.e. Kd = -dlnEd(ed,lu,etc)/d(z)
while the intercept is determined by: lnEd(0-) = lnEd(z)+Kd(z)
Derived surface products include remote sensing reflectances (Rrs), down-welled
attenuation coefficients (Kd) and up- welled attenuation coefficients (Kl). The
units are 1/sr, 1/m and 1/m respectively.
Rrs is calculated as the ratio of the upwelling irradiance just below the
surface (0-) to downwelling radiance just below the surface (0-). The "above
surface" (or "0+") values are derived by simply multiplying a constant of
0.5238.
The attenuation coefficients (Kd & Kl) for the surface were derived by
calculating the average of the top 25 meters of the profiles.
Suspicious data values (i.e. low signals or "spiking") were corrected (or
"flagged") so that users of the data set could determine their usefulness for
their own applications.
These data are a collection of in-situ measurements gathered from the Weatherbird II research vessel during the EDDIES experiment (2004 and 2005).
Contact: David Court (dcourt@icess.ucsb.edu)
Institute for Computational Earth System Science
University of California, Santa Barbara (UCSB)
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