1. Comparison of observed SST Vs. Satellite AVHRR SST
OC LT Steven Malvig

2. Comparison of Observed SST Vs. AVHRR SST
Introduction
Data Collection Methods
Data Analysis
Results
Conclusions
Recommendations

3. Introduction
An accurate SST analysis is essential for the performance of both oceanography and meteorology forecasting models
Buoy and shipboard SST measurements are sparse compared to the abundance of temperature measurements on land
AVHRR Sensors aboard satellites can measure SST on a global scale
But… how accurate are they?

4. Data Collection Methods
Shipboard SST measurements were collected onboard R/V Pt Sur from Jan 31-Feb 4, 2009.
Floating Boom
Sea Chest
Scripps and National Buoy Data Center (NDBC) buoy SST from Jan31-Feb4, 2009 were collected from the NDBC website. (San Francisco, Monterey, Point Sur)
AVHRR (On board NOAA-17 & 18 Polar-orbiting Satellites) SST from Jan 31-Feb4, 2009 were collected and analyzed in TerraScan.

5. Shipboard Measurements
Underway Data Acquisition System (UDAS)
Floating Boom
Sea Chest (Intake)
Data Recorded every 3 Seconds
Boom
Sea Chest

6. Buoy Locations
Station NDBC 18 NM W of SF Bay Location: N W
Station NDBC 27 NM W of Monterey Bay Location: N W
Station SCRIPPS Near Pt Sur. Location: N W

7. NOAA 17 &18 AVHRR AVHRR sensor NOAA-17: launched 24 June 2002
Sun-synchronous orbit
810km above the Earth
Orbits every 101 minutes.
AVHRR Sensor
1.09 km resolution
Nighttime
NOAA-18: Launched 20 May 2005
Sun-synchronous orbit
854km above the Earth
Orbits every 102 minutes
AVHRR Sensor
1.09 km resolution
Daytime
AVHRR measure the reflectance /emittance of the Earth in 5 relatively wide spectral bands.
The first two are centered around red (0.6 micrometer) and near-infrared(0.9 micrometer) regions.
The third is around 3.5 micrometer,
Channels 4/5 sample the thermal radiation emitted by the planet,
Channel 4: μm – 0.12K
Channel 5: μm – 0.12K
Channels 4/5 used for SST
AVHRR sensor

8. NOAA 17 &18 AVHRR Transmittance
AVHRR Ch4
AVHRR Ch5
AVHRR Ch3
Channel 4 has a slightly greater transmission band therefore brightness temperatures are slightly higher than channel 5
MCSST= (T4) (Tf)(T4-T5) (T4-T5)(sec(q) – 1.0) –
Where T4 & T5 are the brightness temperatures in K, sec(q) is the zenith angle, and Tf is the analyzed field temperature.

9. Sample Imagery
Channel 4
Channel 5

10. Data Analysis
Cruise Path SST (Boom)

11. AVHRR SST @ Ship Location
Data Analysis
AVHRR Ship Location

12. Time Series of SST Observations

13. Time Lapse of AVHRR SST Passes w/Ship Location
Jan 31

14. Time Lapse of AVHRR SST Passes w/Ship Location
Jan 31

15. Time Lapse of AVHRR SST Passes w/Ship Location
Jan 31

16. Time Lapse of AVHRR SST Passes w/Ship Location
Jan 31

17. Jan 31

18. Feb 1

19. Feb 1

20. Feb 1

21. Feb 1

22. Feb 1

23. Feb 1

24. Feb 2

25. Feb 2

26. Feb 2

27. Feb 2 Warmest SST recorded: (C°) 14.3 (Pt Sur Buoy) 13.8 (AVHRR)
Feb 2 (1355 PST)
SST increased 1.8 degrees (C) in 4 hours from 12.5 to 13.8 buoy measured. 1.2 degrees from 12.7 to 13.8 as measured by AVHRR What is this? Then decreased back to 12.9 (buoy) and 11.8 AVHRR 7 hours later
Station SCRIPPS Near Pt Sur. Location: N W
Feb 2

28. Feb 3

29. Feb 3

30. Fog Bank
Feb 3

31. Fog Bank
Feb 3

32. Feb 4

33. Feb 4

34. Cloudy!
Feb 4

36. 2 Feb 1355 (PST)

41. Difficult to tell with so few samples if one sensor out performs the other.

44. Statistical Analysis ALL Observed and AVHRR SST (C°) MEAN ST DEV
All AVHRR SST
11.41
0.74
All Observation SST
11.88
0.57
Differences between observed and AVHRR (C°)
SF Buoy - AVHRR
+0.46
0.37
PT Sur Buoy - AVHRR
+0.30
0.36
Monterey Buoy - AVHRR
+0.34
0.39
SST Boom - AVHRR
+0.42
0.42
Total of Observed - AVHRR
+0.44

45. Conclusions AVHRR is a relatively accurate source of SST measurements
A mean of 0.44 (C°) less than Shipboard/Buoy measurements (ST DEV = 0.36 (C°) )
Almost always cooler than observed
Greater fluctuations in AVHRR
Possible affects from Water Vapor
Small sample size makes determinations inconclusive
No appreciable difference between NOAA 17 & 18 sensors
AVHRR can not see through clouds!

46. Recommendations Larger sample size Longer period: Larger spatial area
Need more than 25!
Difficult to be conclusive with so few samples
Longer period:
More satellite passes/observations
Larger spatial area
AVHRR is a Global satellite
Intra-Seasonal
Understand the role of water vapor

47. Questions?