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

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.

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

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)

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.

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.

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

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

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

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

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)

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)

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

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

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.

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.

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.

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? -.36 Mean SST Difference -.84 LW Radiance Difference: ~50 W/m^2

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.

Questions? LCDR Jake Hinz 656-1043