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Physical Sciences and Mathematics Commons™

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Geology

Portland State University

Series

1994

Articles 1 - 2 of 2

Full-Text Articles in Physical Sciences and Mathematics

A Method For Determining Ice-Thickness Change At Remote Locations Using Gps, Christina L. Hulbe, I. M. Whillans Jan 1994

A Method For Determining Ice-Thickness Change At Remote Locations Using Gps, Christina L. Hulbe, I. M. Whillans

Geology Faculty Publications and Presentations

Ice-thickness changes at remote locations on ice sheets can be determined by means of precise Global Positioning System (GPS) surveys with interferometric solutions. Remote sites are precisely surveyed relative to GPS receivers on rock. Repeat observations of the position of a remote site provide its vertical velocity. The difference between this velocity and accumulation rate is an indicator of change in ice-sheet thickness. Allowance must be made for the movement of survey markers due to firn compaction and down-slope ice motion, To allow for firn compaction, very long- poles arc placed to a sufficient depth in the firn that the …

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Evaluation Of Strain Rates On Ice Stream B, Antarctica, Obtained Using Differential Gps, Christina L. Hulbe, I. M. Whillans Jan 1994

Evaluation Of Strain Rates On Ice Stream B, Antarctica, Obtained Using Differential Gps, Christina L. Hulbe, I. M. Whillans

Geology Faculty Publications and Presentations

The "stop-and-go" kinematic Global Positioning System (CPS) technique was used to survey 270 stations twice within a 25 km by 10 km strain grid on the surface of Ice Stream B. One or two geodetic quality receivers operated as reference pivots, while two similar receivers traveled to grid stations. Each station was occupied for 25 s. The method is rapid and reliable. Each survey was completed within 2 weeks. Calculated horizontal strain rates are accurate to 1%. Relative vertical velocities are accurate to 20 mm kmI a-1. Maps of the four horizontal velocity gradients, relative vertical velocity and surface elevation …

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