W. Emery | University of Colorado, Boulder (original) (raw)

Papers by W. Emery

We investigate the wind driven velocity structure of the California Current (CC) using a 12-year ... more We investigate the wind driven velocity structure of the California Current (CC) using a 12-year time series of ageostrophic velocities, ocean surface winds, and two regression models of the system. The ageostrophic current is estimated by removing geostrophic velocities, which are determined by the combination of CTD (conductivity, temperature, depth) and altimetry data from total flow velocity observations. Total current

Journal of Geophysical Research, 1995

Correction to “A comparison of solar tides derived from UARS high-resolution Doppler imager wind ... more Correction to “A comparison of solar tides derived from UARS high-resolution Doppler imager wind measurements with simulations from the NCAR thermosphere-ionosphere-mesosphere electrodynamics general circulation model” by Dong L. Wu, Paul B. Hays, and Raymond G. Roble

International Society for Photogrammetry and Remote Sensing (ISPRS) Book Series, 2004

IGARSS '96. 1996 International Geoscience and Remote Sensing Symposium

ABSTRACT

The generation of climate data records (CDRs) is a critical step in providing the necessary infor... more The generation of climate data records (CDRs) is a critical step in providing the necessary information for scientists, decision-makers, and stakeholders to make adaptive choices that could improve the nation's resiliency to environmental change and variability, maintain our economic vitality, and improve the safety and comfort of U.S. citizens. These CDRs are particularly needed for the Arctic, where existing evidence

Bulletin of the American Meteorological Society, 1995

... Aagaard, K., and EC Carmack, The Role of Sea Ice and Other Fresh Water in the Arctic Circulat... more ... Aagaard, K., and EC Carmack, The Role of Sea Ice and Other Fresh Water in the Arctic Circulation, - *HRSK\V 5HV , 94, C10, 14485 ... Emery, WJ, CW Fowler and JA Maslanik, Satellite Derived Maps of Arctic and Antarctic Sea Ice Motion: 1988 1994, *HRSK\V 5HV /HWW , 24, 8 ...

IEEE International IEEE International IEEE International Geoscience and Remote Sensing Symposium, 2004. IGARSS '04. Proceedings. 2004

The Maximum Cross Correlation (MCC) method is used with infrared and passive microwave images of ... more The Maximum Cross Correlation (MCC) method is used with infrared and passive microwave images of sea surface temperature (SST) along with ocean color images to compute sea surface currents from sequential imagery. These surface currents are then merged with geostrophic surface currents computed from coincident satellite altimetry observations to yield a high spatial resolution map of the surface mesoscale currents

TOPEX/POSEIDON science investigations plan, 1991

ABSTRACT

Gayana

Surface coastal currents off California are a good example of the complex variability in space an... more Surface coastal currents off California are a good example of the complex variability in space and time of currents in an ocean basin eastern boundary. Conventional oceanographic measurements are unable to resolve these relatively small scale variations but by employing both satellite imagery and satellite altimetry we are able to resolve this complex structure and its variations in space and time. Moreover using historical satellite imagery we are able to extend this study back into the past. Our emphasis will be on resolving these variations and later studies will relate these variations to various forcing functions.

Proceedings of IGARSS '94 - 1994 IEEE International Geoscience and Remote Sensing Symposium, 1994

Heat transfer and ice production in the ice-covered seas is controlled to a large extent by ice m... more Heat transfer and ice production in the ice-covered seas is controlled to a large extent by ice motion, which is in turn a function of winds and atmospheric boundary layer conditions. While sea-ice models appear to capture the general elements of this interaction, relatively little data have been available to verify model performance or to assess the spatial and temporal variability of ice motion. Several satellite remote sensing instruments provide the capability of detecting ice displacements. In combination with drifting buoy data, it is now possible to create detailed motion fields suitable for studying mesoscale responses of the ice pack to wind forcing. AVHRR, SAR, and drifting buoys have been merged using optimal interpolation techniques to generate daily gridded ice velocity fields for the Beaufort Sea from June 1992 thru July 1993. These motion fields are compared to simulations using a dynamic-thermodynamic ice model with different ice rheologies and heat transfer processes. The motion fields are discussed in terms of responses to various atmospheric synoptic regimes, and sources of differences between observed and simulated motions are considered. The remotely-sensed ice motion fields show seasonal and temporal variability not apparent in the relatively widely-spaced buoy network. Ice velocities and divergence rates agree in general with the simulations. The cavitating fluid and viscous-plastic ice rheologies yield similar drift directions, but can differ substantially in drift speed under strong winds. The overall utility of AVHRR-based ice motion fields is discussed. Possibilities of assimilating the daily motion fields directly into the ice model to assist in refining the thermodynamic portion of the model is described

Mapping the mesoscale surface velocity stream function by combining estimates of surface height f... more Mapping the mesoscale surface velocity stream function by combining estimates of surface height from satellite altimetry and surface currents from sequential infrared (sea-surface temperature) imagery using optimal interpolation is described. Surface currents are computed from infrared images by the method of maximum crosscorrelations (MCC) and are combined with altimeter sealevel anomaly data from the TOPEX/Poseidon and ERS satellites. The analysis method was applied to 6 years of data from the East Australian Current region. The covariance of velocity and sea-level data is consistent with the statistical assumptions of homogeneous, isotropic turbulence, with typical length scales of order 220 km and time scales of 10 days in this region. Augmenting the analysis of altimeter data with MCC velocity observations improves the resolution of the surface currents, especially near the Australian coast, and demonstrates that the two data sources provide consistent and complementary observations of the surface mesoscale circulation. The volume of MCC data is comparable to that from a satellite altimeter, but with a more variable distribution of spatial and temporal resolution. In concert with altimetry, satellite radiometer velocimetry represents a technique useful for retrospective analysis of currents from high-resolution satellite radiometer data-sets.

As one of the few places in the ocean where winter cooling/mixing creates conditions where water ... more As one of the few places in the ocean where winter cooling/mixing creates conditions where water from the surface can penetrate into the deep ocean the Labrador Sea is an area of interest to people studying climate change in the ocean. Persistent cloud cover over this area makes it impossible to use infrared satellite imagery to relate space/time changes in

Coastal surface currents have been computed for years from sequential infrared and more recently ... more Coastal surface currents have been computed for years from sequential infrared and more recently ocean color imagery using the Maximum Cross Correlation (MCC) technique. Preliminary results suggest that this MCC method may be applied to sequential Synthetic Aperture Radar (SAR) imagery yielding surface currents with a much higher spatial resolution which are independent of the presence of cloud cover which makes it impossible to use infrared or ocean color imagery. A requirement for the application of the MCC to SAR imagery is the presence of surface slicks, which are often related to ocean color patterns. Test applications are made to ENVISAT ASAR images. 0-7803-9510-7/06/$20.00

Several Earth observation satellites acquire images with different spatial resolutions, e.g., a p... more Several Earth observation satellites acquire images with different spatial resolutions, e.g., a panchromatic band with high resolution, and spectral bands with lower resolution. Likewise, we often face the problem of the presence of different resolutions when performing joint analyses of images acquired by different satellites. This paper presents a methods for unsupervised change detection of multiresolution images. The approach is based on the concept of a reference resolution, corresponding to the highest resolution in the dataset. The spatial relationships between the class labels are specified through a Markov random field model defined at the reference resolution. Data at coarser scales are modelled as mixed pixels by relating the observations to the classes at the reference resolution. A Bayesian framework for classification based on this multiscale model is adopted. The classification is performed by an "iterative conditional modes" (ICM) algorithm. A computationally efficient scheme for parameter estimation based on a combination of the ICM and of the expectationmaximization algorithm is used. Results obtained on real satellite images are presented.

We investigate the wind driven velocity structure of the California Current (CC) using a 12-year ... more We investigate the wind driven velocity structure of the California Current (CC) using a 12-year time series of ageostrophic velocities, ocean surface winds, and two regression models of the system. The ageostrophic current is estimated by removing geostrophic velocities, which are determined by the combination of CTD (conductivity, temperature, depth) and altimetry data from total flow velocity observations. Total current

Journal of Geophysical Research, 1995

Correction to “A comparison of solar tides derived from UARS high-resolution Doppler imager wind ... more Correction to “A comparison of solar tides derived from UARS high-resolution Doppler imager wind measurements with simulations from the NCAR thermosphere-ionosphere-mesosphere electrodynamics general circulation model” by Dong L. Wu, Paul B. Hays, and Raymond G. Roble

International Society for Photogrammetry and Remote Sensing (ISPRS) Book Series, 2004

IGARSS '96. 1996 International Geoscience and Remote Sensing Symposium

ABSTRACT

The generation of climate data records (CDRs) is a critical step in providing the necessary infor... more The generation of climate data records (CDRs) is a critical step in providing the necessary information for scientists, decision-makers, and stakeholders to make adaptive choices that could improve the nation's resiliency to environmental change and variability, maintain our economic vitality, and improve the safety and comfort of U.S. citizens. These CDRs are particularly needed for the Arctic, where existing evidence

Bulletin of the American Meteorological Society, 1995

... Aagaard, K., and EC Carmack, The Role of Sea Ice and Other Fresh Water in the Arctic Circulat... more ... Aagaard, K., and EC Carmack, The Role of Sea Ice and Other Fresh Water in the Arctic Circulation, - *HRSK\V 5HV , 94, C10, 14485 ... Emery, WJ, CW Fowler and JA Maslanik, Satellite Derived Maps of Arctic and Antarctic Sea Ice Motion: 1988 1994, *HRSK\V 5HV /HWW , 24, 8 ...

IEEE International IEEE International IEEE International Geoscience and Remote Sensing Symposium, 2004. IGARSS '04. Proceedings. 2004

The Maximum Cross Correlation (MCC) method is used with infrared and passive microwave images of ... more The Maximum Cross Correlation (MCC) method is used with infrared and passive microwave images of sea surface temperature (SST) along with ocean color images to compute sea surface currents from sequential imagery. These surface currents are then merged with geostrophic surface currents computed from coincident satellite altimetry observations to yield a high spatial resolution map of the surface mesoscale currents

TOPEX/POSEIDON science investigations plan, 1991

ABSTRACT

Gayana

Surface coastal currents off California are a good example of the complex variability in space an... more Surface coastal currents off California are a good example of the complex variability in space and time of currents in an ocean basin eastern boundary. Conventional oceanographic measurements are unable to resolve these relatively small scale variations but by employing both satellite imagery and satellite altimetry we are able to resolve this complex structure and its variations in space and time. Moreover using historical satellite imagery we are able to extend this study back into the past. Our emphasis will be on resolving these variations and later studies will relate these variations to various forcing functions.

Proceedings of IGARSS '94 - 1994 IEEE International Geoscience and Remote Sensing Symposium, 1994

Heat transfer and ice production in the ice-covered seas is controlled to a large extent by ice m... more Heat transfer and ice production in the ice-covered seas is controlled to a large extent by ice motion, which is in turn a function of winds and atmospheric boundary layer conditions. While sea-ice models appear to capture the general elements of this interaction, relatively little data have been available to verify model performance or to assess the spatial and temporal variability of ice motion. Several satellite remote sensing instruments provide the capability of detecting ice displacements. In combination with drifting buoy data, it is now possible to create detailed motion fields suitable for studying mesoscale responses of the ice pack to wind forcing. AVHRR, SAR, and drifting buoys have been merged using optimal interpolation techniques to generate daily gridded ice velocity fields for the Beaufort Sea from June 1992 thru July 1993. These motion fields are compared to simulations using a dynamic-thermodynamic ice model with different ice rheologies and heat transfer processes. The motion fields are discussed in terms of responses to various atmospheric synoptic regimes, and sources of differences between observed and simulated motions are considered. The remotely-sensed ice motion fields show seasonal and temporal variability not apparent in the relatively widely-spaced buoy network. Ice velocities and divergence rates agree in general with the simulations. The cavitating fluid and viscous-plastic ice rheologies yield similar drift directions, but can differ substantially in drift speed under strong winds. The overall utility of AVHRR-based ice motion fields is discussed. Possibilities of assimilating the daily motion fields directly into the ice model to assist in refining the thermodynamic portion of the model is described

Mapping the mesoscale surface velocity stream function by combining estimates of surface height f... more Mapping the mesoscale surface velocity stream function by combining estimates of surface height from satellite altimetry and surface currents from sequential infrared (sea-surface temperature) imagery using optimal interpolation is described. Surface currents are computed from infrared images by the method of maximum crosscorrelations (MCC) and are combined with altimeter sealevel anomaly data from the TOPEX/Poseidon and ERS satellites. The analysis method was applied to 6 years of data from the East Australian Current region. The covariance of velocity and sea-level data is consistent with the statistical assumptions of homogeneous, isotropic turbulence, with typical length scales of order 220 km and time scales of 10 days in this region. Augmenting the analysis of altimeter data with MCC velocity observations improves the resolution of the surface currents, especially near the Australian coast, and demonstrates that the two data sources provide consistent and complementary observations of the surface mesoscale circulation. The volume of MCC data is comparable to that from a satellite altimeter, but with a more variable distribution of spatial and temporal resolution. In concert with altimetry, satellite radiometer velocimetry represents a technique useful for retrospective analysis of currents from high-resolution satellite radiometer data-sets.

As one of the few places in the ocean where winter cooling/mixing creates conditions where water ... more As one of the few places in the ocean where winter cooling/mixing creates conditions where water from the surface can penetrate into the deep ocean the Labrador Sea is an area of interest to people studying climate change in the ocean. Persistent cloud cover over this area makes it impossible to use infrared satellite imagery to relate space/time changes in

Coastal surface currents have been computed for years from sequential infrared and more recently ... more Coastal surface currents have been computed for years from sequential infrared and more recently ocean color imagery using the Maximum Cross Correlation (MCC) technique. Preliminary results suggest that this MCC method may be applied to sequential Synthetic Aperture Radar (SAR) imagery yielding surface currents with a much higher spatial resolution which are independent of the presence of cloud cover which makes it impossible to use infrared or ocean color imagery. A requirement for the application of the MCC to SAR imagery is the presence of surface slicks, which are often related to ocean color patterns. Test applications are made to ENVISAT ASAR images. 0-7803-9510-7/06/$20.00

Several Earth observation satellites acquire images with different spatial resolutions, e.g., a p... more Several Earth observation satellites acquire images with different spatial resolutions, e.g., a panchromatic band with high resolution, and spectral bands with lower resolution. Likewise, we often face the problem of the presence of different resolutions when performing joint analyses of images acquired by different satellites. This paper presents a methods for unsupervised change detection of multiresolution images. The approach is based on the concept of a reference resolution, corresponding to the highest resolution in the dataset. The spatial relationships between the class labels are specified through a Markov random field model defined at the reference resolution. Data at coarser scales are modelled as mixed pixels by relating the observations to the classes at the reference resolution. A Bayesian framework for classification based on this multiscale model is adopted. The classification is performed by an "iterative conditional modes" (ICM) algorithm. A computationally efficient scheme for parameter estimation based on a combination of the ICM and of the expectationmaximization algorithm is used. Results obtained on real satellite images are presented.