# Presentation: 688843

## Sea Surface Temperature.MOD 28 Status 

**O. B. Brown, P. J. Minnett, R. H. Evans, E. J. Kearns**
**&**
**Viva Banzon, Warner Barringer, Jim Brown, Jennifer Hanafin, Erica Key, Kay Kilpatrick, Ajoy Kumar, Kevin Maillet, Goshka Szczodrak,**
**Sue Walsh.**
**Meteorology and Physical Oceanography**
**Rosenstiel School of Marine and Atmospheric Science**
**University of Miami**

- MODIS Science Team Meeting
- Baltimore, 18 December, 2001

## The need for validation

- The **infrared bands** of MODIS form **self-calibrating radiometers.** The retrieved SST fields are validated to confirm the procedures used to generate them from the radiometer data are performing as believed, *i.e*. it is the **atmospheric correction algorithm that is being validated**.
- This requires **instrumental imperfections** to be **known**** **and the data **corrected**.
- The validation exercise provides a determination of the **accuracy characteristics of the derived fields. **

## ESE Relevance:Decadal SST trends

- From: Casey, K. S. and P. Cornillon (2001). "Global and Regional Sea Surface Temperature Trends." *Journal of Climate* **14**: 3801–3818.

- Based on conventional measurements over ~5 decades.
- Signals are such that if satellite SST’s are accurate to ~0.2K, signals should be detectable over a couple of decades.

## MODIS TERRA NIGHTTIME 11μm SST

**MODIS TERRA ****NIGHTTIME**** 11****μ****m SST**

- -2      5    10  15   20  25  30  35
- oC

- MAY 2001
- V 3.3.1

- MODIS/OCEAN GROUP
- GSFC, RSMAS

## SST Animation

- Seasonal migration
- Tropical Instability Waves
- Monsoon effects in Arabian Sea
- Warm water entering Arctic by Norway
- Gulf Stream.....

## MODIS SST 

## What is SST? – the skin vs. bulk debate

- The optical depth of sea water at infrared wavelengths is < 1mm. The **source of the MODIS signal** in the atmospheric windows is the **skin layer** of the ocean, which is generally cooler than the subsurface layer because of heat flow from the ocean to the atmosphere.
- The **conventional** meaning of **SST** is the temperature measured at a **depth of a meter** or more by a contact thermometer; the so-called bulk temperature.

**At the levels of accuracy at which SST needs to be measured for MODIS, skin and bulk temperatures are not the same.**

## Near surface temperature gradients – ideal, conceptual situation

## Combined effect of skin and diurnal thermocline effects

-  Skin effect responds quickly to changing surface fluxes on time scales of seconds; vertical scale <1mm.
-  Diurnal thermocline integrates fluxes, and responds to changing surface fluxes on time scales of minutes to hours; vertical scale of several m.
-  Signs of effects are usually opposite.

## SkinDeEP  

- Microstructure probes

- _Skin Depth Experimental Profiler_

## Near surface temperature gradients – reality

**Profile measured at 12:51 local time on **
**4 October 1999.  Off Baja California, **
**R/V *****Melville***** MOCE-5 cruise.**
**Blue line = SkinDeEP* profile**
**Blue circle = M-AERI skin temp.**
**Red cross = Float bulk SST at ~0.05m**
**Green star = Ship thermosalinograph at ~3m**

- From  Ward, B. and P. J. Minnett, 2001. An autonomous profiler for near surface temperature measurements. *Gas Transfer at Water Surfaces.* M. A. Donelan, W.M. Drennan, E.S. Saltzmann and R. Wanninkhof (Eds.) *American Geophysical Union Monograph 127.* 167 - 172.

## Time evolution of near-surface thermal gradients 

**SkinDeEP profiles on 12 October 1999.** **Off Baja California,  R/V *****Melville*****.**
- From  Ward, B. and P. J. Minnett, 2001. An autonomous profiler for near surface temperature measurements. *Gas Transfer at Water Surfaces.* M. A. Donelan, W.M. Drennan, E.S. Saltzmann and R. Wanninkhof (Eds.) *American Geophysical Union Monograph 127.* 167 - 172.

## Wind speed dependence of the skin effect

- Note collapse of envelope at moderate to high wind speeds.

## Wind speed dependence of diurnal & skin effects

- Note:  effects of diurnal thermocline effects at low winds

## Wind speed dependence of diurnal & skin effects

- Terra and Aqua overpass times.

## Measurements of skin temperature

- Because of the effects of diurnal thermoclines and the skin layer, **primary validation** of MODIS SST should be by reference to surface-level measurements of **skin temperature**. This can be measured by filter radiometers or spectroradiometers on ships, aircraft or fixed platforms.
- The instruments must be well calibrated to reach the level of <0.1K absolute uncertainties. There are few such instruments available. One of which is the M-AERI......

## MAERI -overview

## Temperatures are traced to NIST

- On-board black-body cavities have thermometers calibrated to NIST-traceable thermometers (SSEC)
- Periodic calibration using a 3rd black body in M-AERI zenith view.
- Periodic calibration of M-AERI system with a NIST-designed Water-Bath Black-Body target at RSMAS, using NIST-traceable reference thermometers.
- RSMAS Water-Bath Black-Body target characterized with NIST EOS TXR

- NIST EOS TXR

- TXR characterizing the RSMAS WBBB

## M-AERI on USCGC Polar Star, March 2000 

## Time-series of M-AERI measurements on Explorer of the Seas

- The *Explorer of the Seas* is a Royal Caribbean Cruise Liner, operating a weekly schedule out of Miami. It is outfitted as an oceanographic and atmospheric research vessel, very suitable for satellite validation. For more details see http://www.rsmas.miami.edu/rccl/.

## M-AERI data from Explorer of the Seas

- As at last Team Meeting.....

## M-AERI data from Explorer of the Seas

## MODIS-M-AERI MatchupsBlue = Mediterranean – April 2000; Red =Pacific – March, April 2001; Pink = Pacific – March, April 2001; Green = Atlantic - Explorer of the Seas.

_***All data***_
**M = 0.20K std= 0.26K **
**N  = 242**

_***Explorer of the Seas***_
**M = 0.15K **
**std= 0.21K **
**N  = 50**

## AVHRR-MAERI SST validation experience

-  254    0.06    0.29

- M-AERI validation of Pathfinder SSTs

- Using skin temperatures
- reduces the uncertainties
- by about a factor of two.
- See Kearns *et al*,  2000,
***Bull. Am. Met. Soc***., **81**, 1525-1536

## Buoy Matchups

## Buoy Matchups

- SST Quality Flag = 0

## MODIS Buoy matchups

## Wind speed criterion for SST validation

- For winds > ~6ms-1, relationship between skin and bulk SSTs becomes quite well behaved, at the level of ~0.1K. In these conditions bulk SST may be used to validate satellite-derived SSTs.
- See  Donlon, C. J.,  P. J. Minnett, C. Gentemann, T. J Nightingale, I. J. Barton, B. Ward and J. Murray, 2002. Towards improved validation of satellite sea surface skin temperature measurements for climate research.  ***J. Climate***. In the press.

## Distribution of wind speed <6ms-1

- Buoy data can be used, with caution, in blue areas

- From Donlon, C. J.,  P. J. Minnett, C. Gentemann, T. J Nightingale, I. J. Barton, B. Ward and J. Murray, 2001. Towards improved validation of satellite sea surface skin temperature measurements for climate research.  ***J. Climate***. In the press.

## Are MODIS SSTs Validated?

- VALIDATED PRODUCTS: science quality with well defined uncertainties; improvements may still be _are_ ongoing.
- These are high quality products suitable for longer term or systematic scientific studies and publication.  There may _will_ be later improved versions.
- Within the limits of current analyses, (temporal and regional) ..... **YES**.

## Are MODIS SSTs Validated?

**BUT**......
- Sample size is still small
- Some regions under-represented
- Time-series not yet established
- Continued validation into the future to determine effects of instrumental re-configurations

## Future Plans

- Establish reasons for regional and seasonal trends, and correct for these effects
- Prepare for 2002 validation cruises (*Terra* and *Aqua*)
- Prepare *Aqua* SST retrieval algorithm
- Explore SST4  (4 μm) retrievals
- Improve SST retrieval accuracies

## Trans-oceanic sections

- USCG Ice-breakers across the Pacific, twice each year

- Research cruises, e.g. NOAA S *Ronald H. Brown*

- Container vessels, e.g. SAFMARINE -  USA to SA along WOCE AX8 in Atlantic, several times each year

## Repeat Hydrographic Sections

## Conclusions

- M-AERI provides a critical validation tool for MODIS SST
- Buoys provide a valuable secondary validation, numbers allow sampling a wider selection of environmental variability
- Initial, preliminary SST validation shows *Terra *MODIS comparable to best AVHRR
- Need to establish lack of seasonal and regional biases
- Need to validate experimental SST4 fields
- Need to prepare for *Aqua* MODIS at launch SST algorithm.

## pminnett@rsmas.miami.edu