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Home > Outreach Materials > Posters > Geologists' Tools Poster Image Descriptions |
| Geodesy Poster Description |
NASA satellites are measuring the size and shape of the Earth, as well as its gravity field, to unprecedented accuracy. Modern geodetic techniques such as laser and radar altimetry, interferometric synthetic aperture radar (InSAR), and satellite-to-satellite ranging permit detection of subtle changes in the Earth’s system. Images on the poster illustrate several applications of these methods.
The Jason sea surface height anomaly image shows changes in ocean topography over a ten-day period in September 2005. These data provide information about changes in ocean currents over that time. The improvement to topographic maps derived from satellite data is shown by comparing a Shuttle Radar Topography Mission (SRTM) map of the Central Amazon basin to a map of the same area from GTOPO-30, the best publicly available topographic data prior to the SRTM mission. Laser altimeter (GLAS instrument) measurements from the ICESat mission for a satellite track passing over this region are plotted comparing GLAS and SRTM measurements. GLAS measurements have provided the most accurate digital elevation models (DEMs) ever obtained for the Greenland and Antarctic Ice Sheets (not shown here). The new Gravity Recovery and Climate Experiment (GRACE) have provided scientists with the highest resolution and most accurate maps of the Earth’s gravity field ever obtained. Images compare the GRACE-derived gravity model with the much coarser models from pre-GRACE measurements. Such data allow inferences about the internal structure of the Earth. Also, small changes in gravity due to changing conditions beneath the Earth’s surface can be detected. The final two poster images show changes in the hydrology within the Amazon Basin from wet to dry seasons can be derived from GRACE measurements. More recent research has used GRACE measurements to detect changes in polar ice sheets. Back to poster |
| JASON Sea Surface Height Anomaly Map |
| The Jason Global Near-Real Time Sea Surface Height Anomaly image shows very detailed sea surface height variations over the ten-day period ending 9/24/2005. Ocean surface topography influences where and how fast ocean currents flow. Mapping changes in sea surface height over time allows changes in ocean currents to be tracked. Back to poster |
| Land Elevation Map Comparisons |
| The improvement to topographic maps achieved using satellite data is shown by comparing a Shuttle Radar Topography Mission (SRTM) map of the Central Amazon Basin (right) to the GTOPO30 map (left) of the same region. GTOPO30 was the best publicly available topography data prior to SRTM. The SRTM map has 90 m spatial resolution and ~10 m vertical accuracy, a considerable improvement over GTOPO30. Back to poster |
| ICESAT/SRTM Comparison |
| The image compares ICESAT-derived canopy top, ground, and average elevations to SRTM-derived topography for the ground track labeled A-A’ in the SRTM and GTOPO30 maps of the Central Amazon Basin. ICESat laser altimetry has achieved elevation accuracies down to the few centimeter level, far better than previous methods can obtain. Back to poster |
| Gravity Anomaly Map Comparisons |
| The new Gravity Recovery and Climate Experiment (GRACE) satellite-to-satellite ranging measurements yield more accurate and much higher spatial resolution models of gravity field variations than were obtained previously from years of satellite tracking data. The map of Gravity anomalies from about a year of GRACE data (right) shows much finer details than does the gravity anomaly map (left) derived from earlier satellite measurements. Back to poster |
| GRACE-derived Hydrology Maps |
| The Amazon Basin’s water content varies greatly between wet and dry seasons. This causes variations in the region’s gravity field. These GRACE-derived images compare monthly changes in equivalent water thickness from the wet season (left) and dry season (right). Back to poster |
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