Half a century of satellite remote sensing of sea-surface temperature

Sea-surface temperature (SST) was one of the first ocean variables to be studied from earth observation satellites. Pioneering images from infrared scanning radiometers revealed the complexity of the surface temperature fields, but these were derived from radiance measurements at orbital heights and included the effects of the intervening atmosphere. Corrections for the effects of the atmosphere to make quantitative estimates of the SST became possible when radiometers with multiple infrared channels were deployed in 1979. At the same time, imaging microwave radiometers with SST capabilities were also flown. Since then, SST has been derived from infrared and microwave radiometers on polar orbiting satellites and from infrared radiometers on geostationary spacecraft. As the performances of satellite radiometers and SST retrieval algorithms improved, accurate, global, high resolution, frequently sampled SST fields became fundamental to many research and operational activities. Here we provide an overview of the physics of the derivation of SST and the history of the development of satellite instruments over half a century. As demonstrated accuracies increased, they stimulated scientific research into the oceans, the coupled ocean-atmosphere system and the climate. We provide brief overviews of the development of some applications, including the feasibility of generating Climate Data Records. We summarize the important role of the Group for High Resolution SST (GHRSST) in providing a forum for scientists and operational practitioners to discuss problems and results, and to help coordinate activities world-wide, including alignment of data formatting and protocols and research. The challenges of burgeoning data volumes, data distribution and analysis have benefited from simultaneous progress in computing power, high capacity storage, and communications over the Internet, so we summarize the development and current capabilities of data archives. We conclude with an outlook of developments anticipated in the next decade or so

Preliminary results of the comparison of ATSR measurements with in situ sea temperatures

During October and November, 1991, the NATO Research Vessel Alliance sailed from Amsterdam into the western Mediterranean Sea and during this time measurements were made for the validation of ATSR data. This document reports the initial comparison between ATSR measurements and sea-surface temperatures (SSTs) taken along the ship's track by an in situ thermometer at a depth of about 3m

Radiometric measurements of air-sea and air-ice temperature differences in the Arctic

The polar regions are considered to be particularly sensitive to climate change. The complex interactions between the surface and the overlying atmosphere are important aspects of the local heat budget, and through the atmospheric and oceanic general circulations, to global scales. The temperature difference between the surface and the lowest layer of the air is an important parameter in the surface heat budget, but difficult to measure, especially in conditions of mixed sea-ice and open water. Both surface temperature and near-surface air temperature can be determined radiometrically from measurements of the infrared emission spectra of the surface and atmosphere. The use of a Fourier-transform infrared spectroradiometer, the M-AERI (Marine-Atmospheric Emitted Radiance Interferometer) on ships can provide such data

Upper Ocean Heat and Freshwater Budgets

The distributions of upper ocean heat and fresh water (or salinity) have profound consequences on the atmosphere, including the weather and climate that influence many aspects of human societies. While their mean states are reasonably well described (or so we think), the difficulty of making high-accuracy measurements at high spatial and temporal resolution, uniformly distributed around the oceans, limits our knowledge of seasonal, and shorter, variations and constrains our ability to monitor changes over years and decades. This is more the case for salinity than for heat. The freshwater distribution influences the stability of the upper ocean, especially in polar regions. The increasing stability of the ocean at high latitudes associated with enhanced ice melt is believed to portend disruption to the global thermohaline circulation. Improvements in our ability to measure the heat and freshwater budgets and of the fluxes that control them, that will result from better remote sensing and in situ capabilities, will lead to a better understanding of the ocean, atmosphere, and climate system. This will be aided by the development of more realistic and more accurate numerical models capable of simulating the upper ocean and its interactions with the overlying atmosphere

Cloud forcing of surface radiation in the North Water polynya during NOW '98

Measurements taken from the CCGS Pierre Radisson in the North Water Polynya in spring and summer 1998, are used to study the effects of clouds on the longwave and shortwave components of the Arctic surface radiation budget. The clear-sky "baseline" is provided by parametrizations taken from the literature, tuned to the clear-sky measurements taken during the cruise. The effects of clouds are examined in terms of cloud cover, cloud type, solar zenith angle and time of day. A diurnal signal in the cloud cover is found, with minimum values at local noon. The cloud forcing of the surface radiation was found to be mostly negative (i.e., clouds predominantly cool the surface when the sun is in the sky), with strong dependences on the solar zenith angle, cloud amount and whether the sun is obscured by clouds or is in clear sky; the influence of cloud type was secondary to these parameters

AIRS radiance validation over ocean from sea surface temperature measurements

Demonstrates the accuracy of methods and in situ data for early validation of calibrated Earth scene radiances measured by the Atmospheric InfraRed Sounder (AIRS) on the Aqua spacecraft. We describe an approach for validation that relies on comparisons of AIRS radiances with drifting buoy measurements, ship radiometric observations and mapped sea surface temperature products during the first six months after launch. The focus of the validation is on AIRS channel radiances in narrow spectral window regions located between 800-1250 cm/sup -1/ and between 2500 and 2700 cm/sup -1/. Simulated AIRS brightness temperatures are compared to in situ and satellite-based observations of sea surface temperature colocated in time and space, to demonstrate accuracies that can be achieved in clear atmospheres. An error budget, derived from single channel, single footprint matchups, indicates AIRS can be validated to better than 1% in absolute radiance (equivalent to 0.5 K in brightness temperature, at 300 K and 938 cm/sup -1/) during early mission operations. The eventual goal is to validate instrument radiances close to the demonstrated prelaunch calibration accuracy of about 0.4% (equivalent to 0.2 K in brightness temperature, at 300 K and 938 cm/sup -1/)

Chapter 4 Meteorology and Atmosphere–Surface Coupling in and around Polynyas

Polynyas and the overlying atmosphere interact through a series of feedback mechanisms which impart a distinctive polar maritime character to the boundary layer over and downwind of the open water area. Enhanced turbulent fluxes across the ice-free interface introduce heat and moisture into the otherwise cold, dry polar atmosphere, modifying clouds through plume formation and radiative exchanges between the atmosphere and underlying surface. Anthropogenic aerosols of remote origin and local biogenic emissions provide additional direct and indirect radiative forcing, which may also influence precipitation rates, cloud optical depth, and ozone concentration. These combined effects modulate the efficacy of polar regions' ability to act as a “heat sink” for the climate system, establishing a link between the regional polynya meteorology and global conditions. Models, gridded analyses, and remotely-sensed and validating measurements which describe the meteorology and feedback mechanisms in and around polynyas are discussed in this chapter, with an outlook toward future efforts and novel measurement and analytical techniques