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Full-Text Articles in Engineering
Melt Detection In Antarctic Ice Shelves Using Scatterometers And Microwave Radiometers, David G. Long, Lucas B. Kunz
Melt Detection In Antarctic Ice Shelves Using Scatterometers And Microwave Radiometers, David G. Long, Lucas B. Kunz
Faculty Publications
Ku-band dual-polarization radar backscatter measurements from the SeaWinds-on-QuikSCAT scatterometer are used to determine periods of surface freeze and melt in the Antarctic ice shelves. The normalized horizontal-polarization radar backscatter (sigmao) and backscatter polarization ratio are used in maximum-likelihood estimation of the ice state. This method is used to infer the daily ice-surface conditions for 25 study locations located on the Ronne, Ross, Larsen, Amery, Shackleton, and other ice shelves. The temporal and spatial variations of the radar response are observed for various neighborhood sizes surrounding each given location during the study period. Criteria for determining the dates of melt onset …
Microwave Observations Of Daily Antarctic Sea-Ice Edge Expansion And Contraction Rates, David G. Long, Jeffrey R. Allen
Microwave Observations Of Daily Antarctic Sea-Ice Edge Expansion And Contraction Rates, David G. Long, Jeffrey R. Allen
Faculty Publications
Algorithms for estimating sea-ice extent from remotely sensed microwave sensor data can benefit from knowledge of the "a priori" distribution of the daily expansion and contraction of the sea-ice pack. To estimate the probability distribution of daily Antarctic sea-ice extent change, two independent sea-ice datasets are analyzed: sea-ice extent derived from the QuikSCAT scatterometer and ice concentration estimates from the Special Sensor Microwave/Imager. The daily sea-ice advance and retreat is tracked over a four-year period. The distribution of the daily sea-ice advance/retreat from each sensor is similar and is approximately double-exponential. Daily ice-pack statistics are presented.
An Analysis Of Seawinds-Based Rain Retrieval In Severe Weather Events, David G. Long, Jeffrey R. Allen
An Analysis Of Seawinds-Based Rain Retrieval In Severe Weather Events, David G. Long, Jeffrey R. Allen
Faculty Publications
The Ku-band SeaWinds scatterometer estimates near-surface ocean wind vectors by relating measured backscatter to a geophysical model function for the near-surface vector wind. The conventional wind retrieval algorithm does not explicitly account for SeaWinds' sensitivity to rain, resulting in rain-caused wind retrieval error. A new retrieval method, termed "simultaneous wind/rain retrieval," that estimates both wind and rain from rain-contaminated measurements has been previously proposed and validated with Tropical Rain Measuring Mission data. Here, the accuracy of rains retrieved by the new method is validated through comparison with the Next Generation Weather Radar (NEXRAD) in coastal storm events. The rains detected …
Calibrating Seawinds And Quikscat Scatterometers Using Natural Land Targets, David G. Long, Lucas B. Kunz
Calibrating Seawinds And Quikscat Scatterometers Using Natural Land Targets, David G. Long, Lucas B. Kunz
Faculty Publications
The SeaWinds-on-QuikSCAT (QuikSCAT) and SeaWinds-on-ADEOS-2 (SeaWinds) scatterometers measure the normalized radar backscatter (O) of the earth's surface. These identical radar sensors are on different spaceborne platforms in similar orbits. QuikSCAT and SeaWinds data are used to infer near-surface wind vectors, polar sea-ice extent, polar-ice melt events, etc. In order to verify the relative calibration of these sensors, a simple cross calibration based on land backscatter measurements is performed. A first-order polynomial model is used to remove the incidence angle dependence of O for selected regions of the Amazon rainforest and the Sahara Desert. It is shown that the two sensors …
Correlation And Covariance Of Satellite Scatterometer Measurements, David G. Long, Peter K. Yoho
Correlation And Covariance Of Satellite Scatterometer Measurements, David G. Long, Peter K. Yoho
Faculty Publications
Capable scatterometer designs have been developed that seek improved resolution through the use of higher pulse sampling rates. The high sampling rates bring the traditional scatterometry assumption of measurement independence into question. This paper uses fundamental scattering theory to derive general expressions for correlation and covariance between scatterometer measurements and provides practical analysis using current and future instruments as examples. The paper derives expressions for the measurement variance parameter Kp when measurement correlation due to Rayleigh fading effects is present and relates Kp to the statistics of multiple pulse measurements. A function of the transmit signal modulation and receive processing, …
An Assessment Of Seawinds On Quikscat Wind Retrieval, David Draper, David G. Long
An Assessment Of Seawinds On Quikscat Wind Retrieval, David Draper, David G. Long
Faculty Publications
The scatterometer ocean wind retrieval process produces several possible solutions or ambiguities at each point, requiring a separate ambiguity selection step to infer a unique wind vector field. An ambiguity selection error occurs when the selected wind vector is not the closest ambiguity to the true wind. The current ambiguity selection routine for SeaWinds is ad hoc, but performs well under most circumstances. Factors such as instrument noise and rain can also cause the estimated wind flow to deviate from the true wind. A quality assurance (QA) analysis is performed to assess the ambiguity selection effectiveness and noise level of …