We currently deploy five types of sensors which measure Chlorophyll a fluorescence. These are summarized in the following table:
|Click sensor name for link to manufacturer website||WETLabs ECO FLNTU (& puck)||Turner Designs Cyclops 7||Turner Designs Algaewatch||MultiExciter2||Turner Designs Phytoflash3|
|Excitation Wavelength||470 nm||460 nm||430 nm||435 nm||420-530 nm|
|Detection Wavelength||695 nm
@ 80-85 deg.
|620-715 nm @ 90 deg.||> 665 nm @ 90 deg.||650 ~ 1000 nm||640-730 nm @ 90 deg.|
|Accuracy||+/-0.2 ug/L or 3% of reading (greater of)||+/-0.2% FS|
|Sensor Format||Outward looking||Flow through||Flow through||Outward looking||Flow through|
1 As part of a LOBO mooring
2The multi-exciter excites at multiple wavelengths and uses the resulting aborbances to indicate the types of phytoplankton present. The 435nm excitation is used to measure the total Chlorophyll a.
3The primary purpose of the phytoflash instrument is to measures photosynthetic efficiency (fv/fm), however, the initial fluorescence (Fo) measurement made by the Phytoflash can be used as a chlorophyll a measurement.
Of the five different sensor types deployed at the SATURN stations, the FLNTU and MultiExciter are factory calibrated to units of chlorophyll a concentration (ug/L) using a fluorescent dye as a proxy for chlorophyll. The remainder measure chlorophyll a in relative fluorescent units only (rfu’s). Data from these sensors are therefore not directly comparable, both between sensor types and even between deployments of individual sensors of the same sensor type. It is also worth noting that the FLNTU and MultiExciter calibrations against a fluorescent proxy of a laboratory culture may not accurately reflect the in situ chlorophyll a originating from different algal sources in the estuary.
Current quality control protocols attempt to ensure that within individual sensor deployments data are relatable. This is done through monitoring the sensor response to DI water at Saturn03 & Saturn04. These measurements will capture periods of sensor offset or the onset of fouling. It is important to note, however, that the DI readings do not verify that the slope of the response has not changed over time. These sensors have LED light sources and photodiode detectors and are expected to be relatively stable over time.
For some periods of time, monthly water samples are collected from SATURN-03 and SATURN-04 for the measurement of extracted chlorophyll (link to full protocol). These samples are sometimes used to calculate and apply a field calibration to the chlorophyll data to convert it to chlorophyll concentration (ug/L). Because of the dynamic nature of the estuary and shifting conditions known to affect chlorophyll measurements (temperature, turbidity, different algal communities to name a few) these field calibrations should be considered approximate, but they do allow for some degree of comparison of data from different stations/sensors. Details on these calibrations can be found at the links below.
Protocols to allow for the direct comparison of data from different sensors and sensor types are in development. In addition upgrades to the database to more accurately display data (only comprable data on the same plot) and to allow for access to field calibrated data are underway.
Chlorophyll QA/QC Archive
|s1-chlcal01||through July 2012||FLNTU: evaluation of manufacturer calibration|
|s2-chlcal02||Apr. – Oct. 2012||FLNTU: evaluation of manufacturer calibration|
|s2-chlcal01||July – Oct. 2010||FLNTU: evaluation of manufacturer calibration|
|s3-chlcal01_v2||Oct.2010 – Oct.2012||updated version of field calibration against extracted chlorophyll; released August 2016. Replaced s3-chlcal01_v1|
|s3-chlcal02_v2||Aug.2012-Jan2015||updated version of field calibration against extracted chlorophyll; released August 2016. Replaced s3-chlcal02_v1|
|s3-chlcal03_v2||Jan2015-Jan2016||updated version of field calibration against extracted chlorophyll; released August 2016. Replaced s3-chlcal03_v1|
|s3-chlCal04||Jan2016-Aug2016||AlgaeWatch calibration for 2016; sensor recovered & replaced in early August 2016|
|s3_chlCal05||Aug2016-Jan2016||Cyclops 7 chlorophyll fluorometercalibration; sensor deployed Aug2016 through Jan. 2018|
|s3_chlCal06||Feb2016-Jul2018||preliminary calibration for Cyclops 7 chl. fluorometer deployed 1/31/18|
|s3-chl02||7/11/11 – 10/15/11||sensor fouled: corrections for some periods|
|s3-chl01||9/24/10 – 9/28/10||correction for sensor fouling|
|s4-chlcal01-v2||1/1/10 – 1/1/13||updated version of field calibration against extracted chlorophyll; released August 2016. Replaced s4-chlcal01_v1|
|s4-cal02-v2||1/1/13 – 1/1/16||updated version of field calibration against extracted chlorophyll; released August 2016. Replaced s4-chlcal02_v1|
|s4-chl10||4/13/12 – 7/13/12||shift in sensor response|
|s4-chl09||10/22/10 – 12/13/10||sensor fouled: no correction|
|s4-chl08||8/4/10 – 8/12/10||correction for sensor fouling|
|s4-chl07||7/25/10 – 7/29/10||correction for sensor fouling|
|s4-chl06||7/18/10 – 7/21/10||correction for sensor fouling|
|s4-chl05||6/30/10 – 7/12/10||sensor fouled: no correction|
|s4-chl04||6/12/10 – 6/17/10||correction for sensor fouling|
|s4-chl03||5/13/10 – 5/19/10||correction for sensor fouling|
|s4-chl02||10/14/09 – 11/23/09||sensor fouled: no correction|
|s4-chl01||10/3/09 – 10/9/09||correction for sensor fouling|
|s7-chl01||1/14/15 – 7/29/15||scaling of sensor output to align with later data from the station|
|s10-chl02||8/28/16-12/16/16||alignment of sensor output from cyclops and FLNTU flourometers|