Effects of foam on ocean surface microwave emission inferred from radiometric observations of reproducible breaking waves

Includes bibliographical references.WindSat, the first satellite polarimetric microwave radiometer, and the NPOESS Conical Microwave Imager/Sounder both have as a key objective the retrieval of the ocean surface wind vector from radiometric brightness temperatures. Available observations and models to date show that the wind direction signal is only 1-3 K peak-to-peak at 19 and 37 GHz, much smaller than the wind speed signal. In order to obtain sufficient accuracy for reliable wind direction retrieval, uncertainties in geophysical modeling of the sea surface emission on the order of 0.2 K need to be removed. The surface roughness spectrum has been addressed by many studies, but the azimuthal signature of the microwave emission from breaking waves and foam has not been adequately addressed. RECENtly, a number of experiments have been conducted to quantify the increase in sea surface microwave emission due to foam. Measurements from the Floating Instrumentation Platform indicated that the increase in ocean surface emission due to breaking waves may depend on the incidence and azimuth angles of observation. The need to quantify this dependence motivated systematic measurement of the microwave emission from reproducible breaking waves as a function of incidence and azimuth angles. A number of empirical parameterizations of whitecap coverage with wind speed were used to estimate the increase in brightness temperatures measured by a satellite microwave radiometer due to wave breaking in the field of view. These results provide the first empirically based parameterization with wind speed of the effect of breaking waves and foam on satellite brightness temperatures at 10.8, 19, and 37 GHz.This work was supported in part by the Department of the Navy, Office of Naval Research under Awards N00014-00-1-0615 (ONR/YIP) and N00014-03-1-0044 (Space and Remote Sensing) to the University of Massachusetts Amherst, and N00014-00-1-0152 (Space and Remote Sensing) to the University of Washington. The National Polar-orbiting Operational environmental Satellite System Integrated Program Office supported the Naval Research Laboratory's participation through Award NA02AANEG0338 and supported data analysis at Colorado State University and the University of Washington through Award NA05AANEG0153

Development Of An Improved Microwave Ocean Surface Emissivity Radiative Transfer Model

An electromagnetic model is developed for predicting the microwave blackbody emission from the ocean surface over a wide range of frequencies, incidence angles, and wind vector (speed and direction) for both horizontal and vertical polarizations. This ocean surface emissivity model is intended to be incorporated into an oceanic radiative transfer model to be used for microwave radiometric applications including geophysical retrievals over oceans. The model development is based on a collection of published ocean emissivity measurements obtained from satellites, aircraft, field experiments, and laboratory measurements. This dissertation presents the details of methods used in the ocean surface emissivity model development and comparisons with current emissivity models and aircraft radiometric measurements in hurricanes. Especially, this empirically derived ocean emissivity model relates changes in vertical and horizontal polarized ocean microwave brightness temperature measurements over a wide range of observation frequencies and incidence angles to physical roughness changes in the ocean surface, which are the result of the air/sea interaction with surface winds. Of primary importance are the Stepped Frequency Microwave Radiometer (SFMR) brightness temperature measurements from hurricane flights and independent measurements of surface wind speed that are used to define empirical relationships between C-band (4 - 7 GHz) microwave brightness temperature and surface wind speed. By employing statistical regression techniques, we develop a physical-based ocean emissivity model with empirical coefficients that depends on geophysical parameters, such as wind speed, wind direction, sea surface temperature, and observational parameters, such as electromagnetic frequency, electromagnetic polarization, and incidence angle

Parametric optimal estimation retrieval of the non-precipitating parameters over the global oceans, A

2006 Summer.Includes bibliographical references (pages 82-87).Covers not scanned.Print version deaccessioned 2021.There are a multitude of spacebome microwave sensors in orbit, including the TRMM Microwave Imager (TMI), the Special Sensor Microwave/lmager (SSM/I) onboard the DMSP satellites, the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E), SSMIS, WINDSAT, and others. Future missions, such as the planned Global Precipitation Measurement (GPM) Mission, will incorporate additional spacebome microwave sensors. The need for consistent geophysical parameter retrievals among an ever-increasing number of microwave sensors requires the development of a physical retrieval scheme independent of any particular sensor and flexible enough so that future microwave sensors can be added with relative ease. To this end, we attempt to develop a parametric retrieval algorithm currently applicable to the non-precipitating atmosphere with the goal of having consistent non-precipitating geophysical parameter products. An algorithm of this nature makes is easier to merge separate products, which, when combined, would allow for additional global sampling or longer time series of the retrieved global geophysical parameters for climate purposes. This algorithm is currently applied to TMI, SSM/I and AMSR-E with results that are comparable to other independent microwave retrievals of the non-precipitating parameters designed for specific sensors. The physical retrieval is developed within the optimal estimation framework. The development of the retrieval within this framework ensures that the simulated radiances corresponding to the retrieved geophysical parameters will always agree with observed radiances regardless of the sensor being used. Furthermore, a framework of this nature allows one to easily add additional physics to describe radiation propagation through raining scenes, thus allowing for the merger of cloud and precipitation retrievals, if so desired. Additionally, optimal estimation provides error estimates on the retrieval, a product often not available in other algorithms, information on potential forward model/sensor biases, and a number of useful diagnostics providing information on the validity and significance of the retrieval (such as Chi-Square, indicative of the general "fit" between the model and observations and the A-Matrix, indicating the sensitivity of the model to a change in the geophysical parameters). There is an expected global response of these diagnostics based on the scene being observed, such as in the case of a raining scene. Fortunately, since TRMM has a precipitation radar (TRMM PR) in addition to a radiometer (TMI) flying on-board, the expected response of the retrieval diagnostics to rainfall can be evaluated. It is shown that a potentially powerful rainfall screen can then be developed for use in passive microwave rainfall and cloud property retrieval algorithms with the possibility of discriminating between precipitating and nonprecipitating scenes, and further indicating the possible contamination of rainfall in cloud liquid water path microwave retrievals

The variability and forcing of ocean whitecaps and their impact on air-sea fluxes

The breaking of ocean surface gravity waves is an important phenomenon that affects the dynamics of the upper ocean, development of the wave field, and air-sea exchange processes. As the surface expression of this process, whitecaps provide a visible signature of wave breaking; their areal extent per unit area sea surface - known as the whitecap fraction, W - can be used to quantify the amount and scale of wave breaking. W is traditionally estimated using digital images of the ocean surface and is widely used to represent whitecaps in remote sensing applications, and in the parameterisation of a host of air-sea processes in models. These parameterisations - generally functions of wind speed alone - are based on limited amounts of data, and fail to take into account the known influence of secondary factors on whitecaps. A novel approach to estimating W using satellite observations has recently been developed, based on passive radiometric measurements of brightness temperature at microwave frequencies. The satellite-based approach enables measurement of W on a global scale, and in a variety of conditions. In this work, the basic characteristics of W estimates at two different radiometric frequencies, W10 (10 GHz) and W37 (37 GHz), is investigated. The wind speed dependence, global distribution, and seasonal dependence of the estimates are investigated. Comparison is made against estimates obtained from simple, but widely used, wind speed only parameterisations formulated from in situ data. A more direct comparison of radiometric and photographic W estimates, based on ship-satellite matchups, is also made. Both comparisons indicate that satellite-based W has a different wind speed dependence, resulting in estimates that are, on average, higher at low wind speeds and lower at higher wind speeds than parameterisations formulated from in situ, photographic measurements. On a global scale, this results in satellite-based W being more uniform latitudinally than predictions from traditional formulations. A dataset comprising estimates of W10 and W37, together with collocated and concurrent estimates for a variety of forcing parameters, is used to investigate the the influence on W10 and W37 of secondary forcings, such as the wave field and environmental factors. It is found that on a global scale wind speed describes much of the variability in both W10 and W37 though the influence of secondary factors on W can be appreciable (especially for W37). Based on the magnitude of the influence of secondary forcing factors on W10 and W37, it is concluded that much of the variability in whitecap fraction is likely due to the behavior of the thinner, decaying foam patches, variability that is not captured by the retrieval using the 10 GHz channel. Though whitecap fraction offers a pragmatic approach to inferring the magnitude of processes associated with breaking surface waves, it remains an indirect measure with inherent limitations. More fundamental questions regarding the interpretation and use of W are considered. A dynamical model that relates whitecap fraction to breaking wave statistics is used to illustrate the contribution to whitecap fraction due to whitecaps in different lifetime stages. Such a model provides a framework for better relating whitecap fraction to the dynamic, active part of the wave breaking process which is likely more closely linked to processes such as breaking-induced energy dissipation, turbulent mixing, and bubble-mediated gas exchange. Finally, the implications of use of radiometric estimates for quantifying air-sea processes - specifically production of sea spray aerosol and bubble-mediated gas exchange - is discussed. It is shown that difference between the satellite-based W estimates and those predicted using traditional parameterisations provides an explanation for the consistent geographical biases in sea spray aerosol concentration found in a number of large scale models. The benefit of these novel observations will also extend to predictions of other air-sea processes, and remote sensing applications, that require estimation of W; these benefits will be enhanced if whitecaps and their radiometric signature are more closely related to the physical processes which they are used to quantify

Third Annual Earth Resources Program Review. Volume 3: Hydrology and oceanography

Conference proceedings on hydrology and meteorology investigations under Earth Resources Program - Vol.

Earth Resources: A continuing bibliography with indexes

This bibliography lists 475 reports, articles and other documents introduced into the NASA scientific and technical information system between January 1 and March 31, 1984. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economical analysis

Remote sensing in the coastal and marine environment. Proceedings of the US North Atlantic Regional Workshop

Presentations were grouped in the following categories: (1) a technical orientation of Earth resources remote sensing including data sources and processing; (2) a review of the present status of remote sensing technology applicable to the coastal and marine environment; (3) a description of data and information needs of selected coastal and marine activities; and (4) an outline of plans for marine monitoring systems for the east coast and a concept for an east coast remote sensing facility. Also discussed were user needs and remote sensing potentials in the areas of coastal processes and management, commercial and recreational fisheries, and marine physical processes

Microwave scattering from surf zone waves

Wave breaking in the surf zone is an important forcing mechanism on the generation of nearshore currents and in the driving of sediment transport. At the same time, wave breaking can have significant spatial and temporal variability that needs to be accounted for in the description of nearshore processes. Remote sensors are best suited to collect wave breaking measurements due to their large footprint and synoptic capabilities, but in order to extract quantitative wave parameters a proper understanding of the imaging mechanisms is essential. Microwave sensors have been shown to be able to measure wave parameters in deep water, but in the surf zone many of the assumptions the algorithms are based upon do not hold. Additionally, the dynamics of breaking waves are different and may affect in a yet determined way the signal. This dissertation first intends to address an observational gap regarding surf zone microwave measurements. A novel combination of synchronous, large coverage marine radar, calibrated pulsed Doppler radar and video observations from a field site enable the analysis of the evolution and characteristics of the wave signature. The combined data sets yield superior discrimination rates between breaking and non-breaking waves. Discrimination also allows the study of the microwave scattering by source, where active breaking is separated from remnant foam and steepening waves. Results show that the backscattered power from breaking waves, specifically from the wave roller, is a several dB larger than that of foam and steepening waves and independent of the environmental conditions and polarization state. While similar results have been obtained for deep water waves and variety of scattering models have been proposed, it is found that none of the models can describe all the data. Additionally, most of the models neglect the roller morphology. Therefore, in the last section a scattering model is introduced, in which the roller is treated as a volume where a collection of water droplets embedded in air can scatter incoherently. Multiple interactions of the scattered fields between particles and the boundaries are also accounted for. Though the model formulation is complex, it depends on a few physical parameters (diameter, volume fraction, medium permittivity) and no calibration constants. Comparison against data shows that the model does a reasonable job in predicting the observed scattering levels, polarization response and grazing angle dependencies, although is not capable to reproduce the maximum scattered levels observed and predicts polarization ratios always less than unity

THE APPLICATION OF REMOTE SENSING TECHNIQUES IN HYDROLOGY

REMOTE SENSING, which may be simplistically defined as ’the collection and interpretation of emitted or reflected radiation from a body’, offers the potential for accurate interpolation of surface data and even for its direct measurement on scales ranging from local to world wide. This dissertation has been written primarily for the hydrologist, engineer, environmentalist or student who needs to measure changes either in space or time of hydrological variables such as water quality, but who has little practical knowledge of remote sensing or how it may be of assistance to him. It may be regarded as a reference document which, as a result of internal cross referencing and comprehensive external subject referencing, should enable the reader to acquire a background knowledge of remote sensing theory which is relevant to his interests, to understand the advantages and difficulties of applying remote sensing techniques to his measurement problem and to obtain further information about remote sensing applications which have already been undertaken within his field of interest. The dissertation centres on the hydrological situation in England and Wales by initially outlining the structure of their water industries. The main hydrological measurement objectives in terms of water resources, water supply, effluent disposal and flood prediction and warning are identified and some advantages of incorporating remote sensing into hydrological measurement programmes are suggested. The physical theory of remote sensing is described and the main methods of collecting and analysing remotely sensed data are given. A topic by topic analysis of the most suitable ways of tackling specific hydrological measurement problems through the use of remote sensing is made and the dissertation concludes with an assessment of the likely future use of remote sensing in hydrological measurement programmes in genera

Earth Resources: A continuing bibliography with indexes, Issue 35

This bibliography list 587 reports, articles, and other documents introduced into the NASA Scientific and Technical Information System between July 1, and September 30, 1982. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economic analysis