GPS World

Tag: mountain elevation

  • GNSS surveys show shift in Mount Rainier summit

    GNSS surveys show shift in Mount Rainier summit

    Climate change is altering summits of the tallest ice-capped mountains in the contiguous United States.

    A new study by Scott Hotaling from the Quinney College of Agriculture and Natural Resources and Eric Gilbertson from Seattle University used differential GNSS measurements, satellite data, laser measurements and historical photographs to document the ways ice-capped summits in the Western United States are being affected by climate change.

    For the last century, there have been five ice-capped summits in the contiguous United States, all in Washington State. The researchers measured the current elevations of the summits and compared their findings to historical surveys and photographs to assess whether their elevations have changed and whether their ice caps are still intact.

    For Mount Rainier, Columbia Crest is no longer its highest point. The new summit is now rock on the mountain’s southwest rim roughly 133 meters away. All five of the historically ice-capped summits have shrunk since 1980, with four of the five shrinking by at least 6 meters (20 feet) from loss of snow and ice.

    As of 2024, only two of the five summits still had perennial ice as their highest point. Free-air temperatures for the ice-capped summits indicate significant late summer warming of 2.75°C since 1950 and increases in summer melt days, with most of the change occurring since the late 1990s.

    “Given the synchronous trends, we offer climate-induced loss of summit ice as the most likely explanation for the observed changes to ice-capped summits in the western United States,” the researchers write in their study.

    (A) Historical (left) and contemporary (right) photographs for each ice-capped summit included in this study. (B) Elevation over time for each ice-capped summit (blue) and the nearest rocky summit (red). (Image: Study authors)
    (A) Historical (left) and contemporary (right) photographs for each ice-capped summit included in this study. (B) Elevation over time for each ice-capped summit (blue) and the nearest rocky summit (red). (Image: Study authors)

    The main GNSS survey tool used was a Spectra ProMark 220 dGNSS equipped with an Ashtech antenna. GNSS measurements of the ice-capped summits hads an accuracy of ±0.03 meters. For each dGNSS survey, the researchers recorded a 1-hour measurement on the ice-capped summit. If a nearby rock summit was at a similar elevation to the ice-capped summit, a 1-hour measurement was also recorded for it.

  • Everest survey succeeds with Trimble GNSS

    Everest survey succeeds with Trimble GNSS

    The Government of Nepal has completed fieldwork for measuring Everest’s height using GNSS equipment from Trimble, including the robust R10 receiver.

    The Survey Department of the Government of Nepal has completed fieldwork for the National Initiative for the Measurement of the Height of Sagarmatha (Mount Everest). The Nepali survey team summited at 3 (local time) May 22, 2019 (by the Nepali calendar, that’s २०७६ जेठ ८, or June 8, 2076).

    The summit team of Chief Survey Officer Khim Lal Gautam and Survey Officer Rabin Karki was supported by mountain guide Tshiring Jangbu and two of his fellow Sherpas.

    The ascent was dark, windy and treacherous — the team had to make optimal use of the limited time that the hazardous conditions and their oxygen supplies afforded. The primary surveying task was to collect GNSS observations with the Trimble R10 GNSS receiver they carried.

    On the summit: Chief Officer Khim Lal Gautam, Survey Officer Rabin Karki, Sherpa Tshiring Jangbu, and the Trimble R10. (Photo: Trimble)
    On the summit: Chief Officer Khim Lal Gautam, Survey Officer Rabin Karki, Sherpa Tshiring Jangbu, and the Trimble R10. (Photo: Trimble)

    Due to the limited time window on the summit, they had essentially one shot at the GNSS observations. The R10 was configured to begin collecting observations on power-up. During training and test observations before the ascent, the R10 had proven to be exceptionally reliable, with no malfunctions.

    Compact size, light weight and durability were important factors for the receiver chosen for the summit observations. The IP67-rated R10 with internal battery weighs 1.12 kg (2.5 lb.) and operates in a temperature range of –40° C to +65° C (–40°F to +149° F). Its solid alloy housing withstands a 1-meter drop. The only concern for the team on the final ascent was to keep the battery and spares warm.

    The R10 recorded 1 hour and 16 minutes of GNSS observations. The static data (observations from GPS, GLONASS, Galileo and BeiDou) was post-processed using Trimble Business Center software together with observations from eight GNSS reference stations established as an active control network for the survey. Several of the reference stations were Trimble NetR9 network receivers with Zephyr Geodetic antennas.

    The team also used a compact ground penetrating radar (GPR) instrument to determine the distance between the top of the ice/snow cap on the summit and the highest point of solid rock beneath.

    Many of the successive accepted heights for Everest have been to the top of the ice cap, which can vary seasonally by several meters. A goal of the survey is to provide heights for both aspects of the peak. An additional reason to establish a new height for Everest is to determine whether, and by how much, the 2015 earthquakes in the region altered the mountain.

    Photo: Trimble
    Photo: Trimble

    While the Nepalese survey team’s GNSS observations on the summit will yield the height, the final orthometric elevation will be achieved by applying an updated gravity model. The gravity model was refined from supporting surveys on the mountain and surrounding region.

    A total of 298 new gravity observations were performed over several years, with companion GNSS observations on each control point. More than 248 kilometers of precise leveling, supplemented with trigonometric leveling, was performed for the network of control and base receiver locations. Instruments employed for these terrestrial surveys included Trimble DiNi levels and S9 total stations.

    Trimble GPS/GNSS instruments have been to the Sagarmatha summit on multiple occasions, including in 1990, 1998, 2005 and 2012. The R10 represents the lightest and most compact of these to date.

    By prior agreement between Nepal and China, the results of the 2019 Nepali survey, and a May 2020 Chinese survey, will be jointly announced. Official results are expected this summer.

    Featured photo: A GNSS reference station network was established before the survey to provide data for post processing, and to support additional surveying and geophysical studies of the region. (Photo: Trimble)