Dataset: Laser Optical Plankton Counter

Data consist of particle counts and sizes measured using a Brooke Ocean Technology Laser Optical Plankton Counter (LOPC) and were collected from vertical casts of up to 200 m in depth.
 
Parameter names, definitions and units:
The following information is from the LOPC Software Operation Manual (see related files and references). The LOPC data files are written as binary files and converted to ASCII during a minimal processing step. Each file contains a set of header information:
 
Header 1: PC DATE-TIME: contains Date and Time as recorded from the logging computer.
 
Header 2: USER SUPPLIED HEADER: contains any information provided by the user about the data
 
Header 3: LOPC SOFTWARE CONFIG: contains information about how the LOPC hardware was configured.
 
Header 4: LOPC FIRMWARE CONFIG: contains information about how the LOPC software was configured.
 
Following the header information, the data stream begins as single lines of information, the file format description is as follows:
 
L1-L4: these four lines contain the 128 bins (32 bins per line) of single element plankton counted during this half-second sample.
L1 0 0 0 0 0 0 6 8 8 7 4 2 3 2 2 7 3 4 5 6 5 3 3 2 1 2 5 7 8 0 0 4
L2 3 2 0 3 0 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
L3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
L4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

L5: system status/engineering data
L5 0 100 31 7 116 0 2550 0 0 2247
Description of the L5 line from the sample above (from left to right)
0 = Snapshot number
100 = Threshold
31 = Sample Number
7 = Flow Counts
116 = Delta Time
0 = Buffer Overrun
2550 = Laser Monitor (LMon in A/D counts)
0 = Electronic Counts
0 = Count Period
2247 = Laser Voltage (LVolt in A/D counts)

C: indicates a line of instrument data from any attached serial instruments. The rate at which this is transmitted by the LOPC, the data it contains, and the data string format is determined by the instrument in use. Typically, this represents a stream of CTD data.
C +20.06602 2.35579 -0.056 0.2600 3.8046

This example shows the output from a CTD.
M: indicates a portion of Multi-Element Plankton (MEP) data, where the form is ‘M Element-Number Scan-Number Scan-Length Peak-Laser Monitor. The MEP data is sent whenever the opportunity is available. Both the binned data (L1-L5 lines) and the Instrument data (C lines) take precedence over MEP data.
M 26 20845 1 32869
M 25 20826 30 291
M 24 20831 21 186
M 4 23768 7 33251
M 3 23760 23 1403
M 2 23761 22 1092

Description of file fields:
Snapshot Indicator: This value indicates whether a snapshot is in progress. A 1 indicates a snapshot is in progress, 0 indicates no snapshot is in progress [Found on L5 lines – position 1]

Threshold: The threshold is used to set a lower limit on signal level detection, which ensures that the LOPC is operating above the “noise level” of internal active components. This improves the accuracy and reliability of detection data. [Found on L5 lines – position 2]

Sample Number: A counter indicating number of samples taken by the LOPC at 2 Hz [Found on L5 lines – position 3]

Flow Counts: The Flow Counts indicate the number of counts within a pre-determined size range within current 0.5-second sample (can be used in combination with Delta Time for flow calculations) [Found on L5 lines – position 4]

Delta Time: Delta Time is the accumulated time for all counts detected in the Flow Counts window to pass through the beam (can be used in combination with Flow Counts for flow calculations) [Found on L5 lines – position 5]

Buffer Overrun:Used to indicate an internal buffer overrun. ”1” if a buffer overrun occurs, “0” otherwise [Found on L5 lines – position 6]

Laser Monitor (LMon): Laser Monitor is the mean laser intensity detected by all 35 elements of the photo-diode array during this 0.5-second sample [Found on L5 lines – position 7]

Laser Voltage (LVolt): Laser Voltage is the input voltage to the laser. This value is a monitor of a laser control circuit that will increase or decrease the laser input voltage as required to maintain a preset level (LMon) [Found on L5 lines – position 10]

Element-Number: Indicates the element within the 35-element photo-diode array to which this line of MEP data pertains [Found on M lines – position 1]

Scan-Number: The Scan-Number is read from a 16-bit internal counter (0-65535) that is incremented every 35 µs to provide a measure of time. The Scan-Number indicates the “time” at which the MEP entered the beam for this element [Found on M lines – position 2]

Scan-Length: Scan-Length indicates the number of scans, or the “length of time,” a portion of a MEP was detected on the element of question [Found on M lines – position 3]

Peak Laser Level: The maximum level of laser light detected on this element during passage of a MEP [Found on M lines – position 4]

Related files and references:
Laser Optical Plankton Counter Operation and Maintenance Manual. 2010. Brooke Ocean Technology (www.brooke-ocean.com).

Herman AW. LOPC post-processing page: http://www.alexherman.com/lopc_post.php. Contains software designed to enable first-time users of the LOPC to process data.

Herman AW, M Harvey. 2006. Application of normalized biomass size spectra to laser optical plankton counter net intercomparisons of zooplankton distributions. Journal of Geophysical Research-Oceans. 111(C5): C05S05.

Herman AW, B Beanlands, EF Phillips. 2004. The next generation of Optical Plankton Counter: the Laser-OPC. Journal of Plankton Research. 26(10): 1135-1145.