Craig Donlon

The Global Ocean Data Assimilation Experiment High-resolution Sea Surface Temperature Pilot Project

A new generation of integrated sea surface temperature (SST) data products are being provided by the Global Ocean Data Assimilation Experiment (GODAE) High-Resolution SST Pilot Project (GHRSST-PP). These combine in near-real time various SST data products from several different satellite sensors and in situ observations and maintain the fine spatial and temporal resolution needed by SST inputs to operational models. The practical realization of such an approach is complicated by the characteristic differences that exist between measurements of SST obtained from subsurface in-water sensors, and satellite microwave and satellite infrared radiometer systems. Furthermore, diurnal variability of SST within a 24-h period, manifested as both warm-layer and cool-skin deviations, introduces additional uncertainty for direct intercomparison between data sources and the implementation of data-merging strategies. The GHRSST-PP has developed and now operates an internationally distributed system that provides operatio...

OSTIA : An operational, high resolution, real time, global sea surface temperature analysis system

A new global, operational, high-resolution, combined sea surface temperature (SST) and sea ice analysis system (OSTIA) has been developed at the Met Office. The output is a daily, global coverage 1/20deg (~6 km) combined SST and sea ice concentration product, which is generated in near-real time. The analysis has been designed to meet the needs of applications requiring high-resolution space-time scales including global numerical weather prediction (NWP) and operational ocean models and to prepare for future high-resolution global and regional forecast systems.

Estimating Sea Surface Temperature from Infrared Satellite and In Situ Temperature Data

Sea surface temperature (SST) is a critical quantity in the study of both the ocean and the atmosphere as it is directly related to and often dictates the exchanges of heat, momentum, and gases between the ocean and the atmosphere. As the most widely observed variable in oceanography, SST is used in many different studies of the ocean and its coupling with the atmosphere. The history of this measurement and how this history led to todays practice of computing SST by regressing satellite infrared measurements against in situ SST observations made by drifting/moored buoys and ships are examined. The fundamental differences between satellite and in situ SST are discussed and recommendations are made for how both data streams should be handled. A comprehensive in situ validation/calibration plan is proposed for the satellite SSTs and consequences of the suggested measurements are discussed with respect to the role of SST as an integral part of the fluxes between the ocean and the atmosphere.

Sea surface salinity structure of the meandering Gulf Stream revealed by SMOS sensor

Measurements from the Soil Moisture Ocean Salinity (SMOS) satellite acquired during 2012 in the western North Atlantic are used to reveal the evolution of the sea surface salinity (SSS) structure of the meandering Gulf Stream with an unprecedented space and time resolution. Combined with in situ surface and profile measurements, satellite-derived surface currents, sea surface height (SSH), surface temperature (SST), and chlorophyll (Chl) data, SMOS SSS observations are shown to coherently delineate meanders pinching off from the current to form well-identified salty- (warm-) and fresh- (cold-) core Gulf Stream rings. A covariance analysis at two locations along the separated Gulf stream path (south of Nova Scotia and in the Gulf Stream Extension) reveals a systematically higher correlation between SSS and sea level variability than between SST and SSH during the warmer half of the year. Within (75°W–40°W; 30°N–50°N), Chl concentration is also found to significantly depend on the SSS as SST increases above 20°C.

An Infrared Sea Surface Temperature Autonomous Radiometer (ISAR) for Deployment aboard Volunteer Observing Ships (VOS)

Abstract The infrared SST autonomous radiometer (ISAR) is a self-calibrating instrument capable of measuring in situ sea surface skin temperature (SSTskin) to an accuracy of 0.1 K. Extensive field deployments alongside two independent research radiometers measuring SSTskin using different spectral and geometric configurations show that, relatively, ISAR SSTskin has a zero bias ±0.14 K rms. The ISAR instrument has been developed for satellite SST validation and other scientific programs. The ISAR can be deployed continuously on voluntary observing ships (VOS) without any service requirement or operator intervention for periods of up to 3 months. Five ISAR instruments have been built and are in sustained use in the United States, China, and Europe. This paper describes the ISAR instrument including the special design features that enabled a single channel radiometer with a spectral bandpass of 9.6–11.5 μm to be adapted for autonomous use. The entire instrument infrared optical path is calibrated by viewing ...

The Miami2001 Infrared Radiometer Calibration and Intercomparison. Part II: Shipboard Results

The second calibration and intercomparison of infrared radiometers (Miami2001) was held at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science (RSMAS) during a workshop held from May to June 2001. The radiometers targeted in these two campaigns (laboratory-based and at-sea measurements) are those used to validate the skin sea surface temperatures and land surface temperatures derived from the measurements of imaging radiometers on earth observation satellites. These satellite instruments include those on currently operational satellites and others that will be launched within two years following the workshop. The experimental campaigns were completed in one week and included laboratory measurements using blackbody calibration targets characterized by the National Institute of Standards and Technology (NIST), and an intercomparison of the radiometers on a short cruise on board the R/V F. G. Walton Smith in Gulf Stream waters off the eastern coast of Florida. This paper reports on the results obtained from the shipborne measurements. Seven radiometers were mounted alongside each other on the R/V Walton Smith for an intercomparison under seagoing conditions. The ship results confirm that all radiometers are suitable for the validation of land surface temperature, and the majority are able to provide high quality data for the more difficult validation of satellitederived sea surface temperature, contributing less than 0.1 K to the error budget of the validation. The measurements provided by two prototype instruments developed for ship-of-opportunity use confirmed their potential to provide regular reliable data for satellite-derived SST validation. Four high quality radiometers showed agreements within 0.05 K confirming that these instruments are suitable for detailed studies of the dynamics of air‐sea interaction at the ocean surface as well as providing high quality validation data. The data analysis confirms the importance of including an accurate correction for reflected sky radiance when using infrared radiometers to measure SST. The results presented here also show the value of regular intercomparisons of ground-based instruments that are to be used for the validation of satellite-derived data products—products that will be an essential component of future assessments of climate change and variability.

Solid-State Radiometer Measurements of Sea Surface Skin Temperature

Abstract Satellite sea surface skin temperature (SSST) maps are readily available from precisely calibrated radiometer systems such as the ERS along-track scanning radiometer and, in the near future, from the moderate-resolution imaging spectroradiometer. However, the use of subsurface bulk sea surface temperature (BSST) measurements as the primary source of in situ data required for the development of new sea surface temperature algorithms and the accurate validation of these global datasets is questionable. This is because BSST measurements are not a measure of the sea surface skin temperature, which is actually observed by a satellite infrared radiometer. Consequently, the use of BSST data for validation and derivation of satellite derived “pseudo-BSST” and SSST datasets will limit their accuracy to at least the rms deviation of the BSST–SSST difference, typically about ±0.5 K. Unfortunately, the prohibitive cost and difficulty of deploying infrared radiometers at sea has prevented the regular collecti...

The calibration and intercalibration of sea-going infrared radiometer systems using a low cost blackbody cavity

Abstract There are many infrared radiometer systems available for the measurement of in situ sea surface skin temperature (SSST). Unfortunately, the marine environment is extremely hostile to optical components, and to ensure the accuracy of SSST measurements, an absolute calibration of instrumentation using an independent calibration reference is required both before and after any sea deployment. During extended deployments it is prudent to have additional regular calibration data to monitor instrument performance characteristics. This paper presents a design for an ambient temperature (278–325 K), wide aperture (100 mm), reference blackbody unit that may be used to calibrate a variety of sea-going infrared radiometer systems both in the laboratory and in the field. The blackbody consists of a spun copper cavity coated with well-characterized high emissivity paint (Mankiewicz Nextel Velvet Coating 811-21) immersed in a water bath that is continuously mixed using a strong water pump. The radiant temperatu...

Sensitivity of the diurnal warm layer to meteorological fluctuations. Part 2 A new parameterisation for diurnal warming

A new diurnal warming parameterisation has been developed which allows the shape of the diurnal sea surface temperature (SST) signal to change in response to meteorological fluctuations during the day based on an extensive examination of over 300 diurnal cycles. The parameterisation estimates the diurnal variation in temperature at the surface and at 1 m over a local day based only on wind and insolation measurements averaged over several different periods of the day. The parameterisation is validated against independent data and is compared against other existing parameterisations. Results show that diurnal warming estimates are more accurate when daily fluctuations in wind and insolation are taken into consideration and the new parameterisation captures some of the variability of the shape of the diurnal SST cycle which other parameterisations are unable to achieve. The parameterisation is currently being trialled in the European Space Agency MEDSPIRATION project (a contribution to the Global Ocean Data...

Global measurement of sea surface temperature from space: some new perspectives

The measurement of global sea surface temperature (SST) from space is well established with 20 years of useful data already acquired, but the more stringent sampling requirements and the higher degree of accuracy now demanded for applications in both climate monitoring and operational oceanography are increasingly difficult to meet with the standard meteorological polar orbiting sensors that have been the basic sensors used for global SST mapping. The established methods and sensors for measuring SST, both in situ and in space, are reviewed, compared, and their major limitations are identified. Mention is made of phenomena which complicate an apparently simple measurement, including diurnal stratification, the presence of clouds and the contamination of the stratosphere by volcanic aerosols. Recent developments in remote sensing of SST are mentioned, noting the improved microwave sensors now becoming available, the calibrated infrared sensors planned for geostationary platforms, and weighing the benefits of merging these data. The conventional buoy-calibration of SST measurements from space is complicated by the variable thermal structure of the upper few metres of the ocean. The recent improvement of radiometers for ship deployment has led to better understanding of the thermal skin of the ocean which suggests a new approach for the validation of SST algorithms based on radiation transfer models. Finally, a future strategy is outlined for combining measurements from many types of sensor in order to achieve the required accuracy and sampling rate of SST data products, and to identify some of the remaining scientific challenges in this field.