1. Comparison of Sea Surface Temperature Collection Methods at Sea
Post-Cruise Data Analysis
Jake Hinz
OC3570
April 4, 2019

2. Introduction SST is an important factor in many applications
±0.5ºC is significant in Duct Height
Navy is looking for the best Automated SST method
IR is prevalent in METOC and AEGIS
Previous Similar Studies had been done
Eckard, Gahard, etc.

3. Introduction ‘Skin’ Methods ‘Bulk’ Methods IR guns
Sense the skin of the water’s surface
Top 50μm to 1mm
‘Bulk’ Methods
Seachest intakes, buckets, booms, CTD

4. Collection Methods Mast IR Probe Skin Method Automated IR Radiometer
Mounted on the Port Bridge Wing
Approx. 10m above water line.
Pointed 45 Degrees away from ship
2 Steradian FOV
Narrow Band (8-12 IR window)

5. Collection Methods Underway Data Acquisition System UDAS Bulk Method
Automated Thermistor
Senses Water drawn from 2.5 m deep seachest (non-engineering)
No warm water effluence from the ship
Possibly affected by hull/bow mixing when vessel is moving.

6. Collection Methods Boom Probe Bulk Method Automated Thermistor
Towed alongside/behind ship
Mounted 1.5 m off port quarter
Senses Water Temp on Surface
No warm water effluence from the ship
Possibly affected by hull/bow mixing when vessel is moving
Sinks to approximately 1m when vessel is not making way.

7. Analysis: General Comparisons
Compared SSTs from each method to:
Air Temperature
Down-welled LW radiance
Wind Speed
Direction
Compared SST Differences Between Methods to Each of the Above
Boom – UDAS
Boom - Mast

8. Analysis: General Comparisons
Boom and UDAS track nicely
Mast much higher in a few places
Day 221 is Port San Luis
Day 221 (PSL) explanation
Warmer, Clearer, Still in Lee, more stratification, cooler surface, warm layer, gets cooler with depth.
SSTs does not confirm cool surface, small mixing may explain difference then.
Will address big variations in Mast at days
218, 220, 221

9. Analysis: General Comparisons
Method
Mean
Std. Dev.
UDAS
16.05
1.14
Boom
16.08
1.15
Mast
16.61
1.37
Boom and UDAS about .03 apart (bias)
Boom and Mast about .53 apart (significant) (and more deviation)
BOOM and UDAS, Corr: .996

10. Analysis: ‘Bulk’ Methods
Boom-UDAS: Mean .03
Positive means Colder than Boom
Warmer means Warmer than Boom
Bias .03
Day 221 (PSL) explanation
Warmer, Clearer, Still in Lee, more stratification
Differences do not show cool layer difinitively, but stratification clearly shown in the data.
UDAS, coolest, then BOOM, then Mast

11. Analysis: ‘Bulk’ Methods
Port San Luis Lee
Day 221 (PSL) explanation
Warmer, Clearer, Still in Lee, more stratification
Variations not clearly understood, probably instrumentation on Mast. (Internal thermometer which calibrates black body)

12. Analysis: ‘Bulk’ Methods
Port San Luis Warming/Clearing
Day 221 (PSL) explanation
Warmer, Clearer, Still in Lee, more stratification
Variations not clearly understood, probably instrumentation on Mast. (Internal thermometer which calibrates black body)

13. Analysis: ‘Skin’ vs. ‘Bulk’
Mean Difference
Mean Standard Deviation
Boom - Mast
-0.53
0.69
Boom - UDAS
0.03
0.11
Negative means Warmer than Boom

14. Analysis: ‘Skin’ vs. ‘Bulk’
Variations
SLO Obvious and discussed before.
Other days not wind related.

15. Analysis: ‘Skin’ vs. ‘Bulk’
Air Temp Spikes
LW Radiance Spikes (independent of W/m^2 measure)
Most likely LW correction factors and instrumentation (internal temp sensors) and algorithms may have a hard time correcting for the changes in LW.
All daytime, all related to SST rise
What could cause this LW variability
1-2/8h coverage (218, 219)
7-8/8ths coverage(221.5)
Daytime allows a significant change in temp rapidly and significant change in LW rapidly.
Other rapid changes form hourly obs confirmed changes.
Slow changes did not show variations in SST difference.

16. Analysis: ‘Skin’ vs. ‘Bulk’
218
219
221
One potential cause of the cloud variations is the warm features we crossed…varying the SST rapidly may cause mixing of the layer and possible decreases in stratification.

17. Analysis: ‘Skin’ vs. ‘Bulk’
General trend of diff based on LW (maybe a correction that was not applied for LW reflections into the IR sensor.

18. Analysis: ‘Skin’ vs. ‘Bulk’
Broken up
Indicates that there may be a definite necessity to correct for LW!
Note the LW differences near the variations mentioned before…Is there possibly a critical threshold over which the Mast is unable to handle the change?
Mean SST Difference -.84
LW Radiance Difference: ~50 W/m^2

19. Summary and Conclusions
Bulk methods provided most consistent measures
M/W: differing depths gave~0.03 °C
Other: <0.5
Skin method requires LW correction
Skin method was highly variable in rapidly varying cloud conditions (>>0.5°C)
Even 1/8 variations had significant impact not seen in bulk methods.
Bulk methods may be a better choice for U/W automated collection with little necessity for correction or dependence on other inputs.
.03 is far less than nearly 2 degree swings for the vast majority of military applications. Differences in Low wind/stratified conditions should be noted for bulk methods and the bias corrected.
Variations in IR temps are too high for military apps, especially because the coastal environment can be variable like that.

20. Questions?
LCDR Jake Hinz