Comparison of observed SST Vs. Satellite AVHRR SST OC3570 LT Steven Malvig

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

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?

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.

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

Buoy Locations Station 46026 NDBC 18 NM W of SF Bay Location: 37.759N 122.833W Station 46042 NDBC 27 NM W of Monterey Bay Location: 36.789N 122.404W Station 46239 SCRIPPS Near Pt Sur. Location: 36.338N 122.101W

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: 10.3-11.3 μm – 0.12K Channel 5: 11.5-12.5 μm – 0.12K Channels 4/5 used for SST AVHRR sensor

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= 0.9367(T4) + 0.0864(Tf)(T4-T5) + 0.5979(T4-T5)(sec(q) – 1.0) – 253.8050 Where T4 & T5 are the brightness temperatures in K, sec(q) is the zenith angle, and Tf is the analyzed field temperature.

Sample Imagery Channel 4 Channel 5

Data Analysis Cruise Path SST (Boom)

AVHRR SST @ Ship Location Data Analysis AVHRR SST @ Ship Location

Time Series of SST Observations

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

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

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

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

Jan 31

Feb 1

Feb 1

Feb 1

Feb 1

Feb 1

Feb 1

Feb 2

Feb 2

Feb 2

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 46239 SCRIPPS Near Pt Sur. Location: 36.338N 122.101W Feb 2

Feb 3

Feb 3

Fog Bank Feb 3

Fog Bank Feb 3

Feb 4

Feb 4

Cloudy! Feb 4

2 Feb 1355 (PST)

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

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

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!

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

Questions?