Light Attenuation along the California Coast

1
Light Attenuation along the California Coast

• By LT Lars Lone
• Completed for OC3570

2
Overview

• Reason for research
• Attenuation revisited
• Data used
• Results
• Conclusions
• Follow on studies

3
Reason for Research

• Thesis research
• Use of hyperspectral imagery in visible to near
  IR range
• Understand more why visibility so limited
• Not really discussed in my other OC classes and
  wanted to look at it more

4
Attenuation

• Beers Law
• Iz Ioexp(-kz)
• Where Iz PAR, Io SPAR, k attenuation, z
  depth
• So k -ln(Iz/ Io)/z

5
Data Used
Sites Used 2,12,23
Sites Used 40,45,46,69
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Data Used

• Data sets taken from local apparent noon
• Mitigates need for use of Snells Law and
  refraction issues
• Looked at
• SPAR
• PAR (photosynthetic active radiation)
• Transmissivity
• Fluorometer

7
Results Station 2

• Attenuation and Par have similar curve shape
• No extreme changes in any of the data sets
  looked at

8
Results Station 12

• Largest variation of attenuation
• Water depth greater here
• Similar Transmissivity and Fluorometer as before
• Interesting values for PAR sensor

9
Results Station 23

• Abnormal attenuation curve
• And lowest variation in attenuation
• Transmissivity and Fluorometer look fairly
  normal
• Par sensor off by factor of 10 compared to
  previous 2 stations.

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Results Station 40

• Attenuation Similar to station 12
• Fluorometer readings remain constant longer
• Interesting spikes in SPAR at same depth
• Note surface PAR as well

11
Results Station 45

• Interesting attenuation shift
• Very short attenuation range
• Large PAR values near surface similar to Station
  23

12
Results Station 46

• Less variation in attenuation
• Interesting PAR results as well
• No significant changes in Fluorometer or
  Transmissivity

13
Results Station 69

• Again, abnormal attenuation results
• PAR sensor has a factor of 10 greater than
  normal once again
• No significant value difference for Fluorometer
  or Transmissivity

14
Conclusions

• Deep water had greater overall attenuation values
• Typical ocean values range from .02-2
• My results agree with this
• Unsure of cause for spike in PAR values at half
  of the sites
• More research needs to be done

15
Future Studies

• Attenuation at times other than local apparent
  noon
• Nearshore vs. offshore
• Attenuation loss due to reflectance vs. absorption