Some features of this site are not compatible with your browser. Install Opera Mini to better experience this site.

Notes from the Field

Trail Breaking Grand Mesa

December 19th, 2018 by Christopher Hiemstra and Ludovic Brucker

Colorado’s Grand Mesa as viewed from a commercial airline flight departing Grand Junction, 5 December 2018.


Ground validation measurements are an important part of working with remote sensing instruments like SWESARR. Snow is dynamic and changes occur as soon as it settles to Earth’s surface. In a dry, windy place like Colorado’s Grand Mesa, snow can move around, be packed into drifts, get intercepted in canopy, sublimate back into the atmosphere, and metamorphose into depth hoar as winter progresses.

Fresh snow blankets Grand Mesa’s trees and ground during an early-season snow measurement campaign.  In the week before we arrived, there was 40-70 cm of new snow.


Ludo Brucker (NASA GSFC / Universities Space Research Association) and Chris Hiemstra (Cold Regions Research and Engineering Laboratory) were on Grand Mesa preparing for NASA SnowEx 2019. During the latter half of November 2018, Grand Mesa was blanketed in 40-70 cm (about 15-27 inches) of new snow from a series of storms. Fortunately, a short break in the weather with clear skies was forecast for the last SWESARR engineering flight. Optimistic plans to take early season measurements on Grand Mesa materialized.

Mike Renner, Grand Mesa Lodge, groomed Grand Mesa’s snowmobile trails for the first time late into the previous evening, which aided our one-day measurement campaign visiting radar corner reflectors used for SWESARR assessment and making measurements under the flight lines.


The only problem was that the flight lines were well out into the west end of Grand Mesa and the early season snow was new and deep. Chances of getting stuck on the way out there were high, especially as the route went uphill from Grand Mesa Lodge perched on the south side of Crag Crest. Fortunately, Grand Mesa Lodge owner Mike Renner grooms Grand Mesa snowmobile trails throughout the winter season and he groomed a route out to the west side of the Mesa the previous evening. On the morning of December 4, Ludo and Chris rode 11 miles to the west end of the Mesa.

A radar corner reflector on Grand Mesa was cleaned for the flight.  Reflectors are used to return strong radar signals back to the aircraft.


Just as they arrived in the blazing sun, the drone of the Twin Otter carrying SWESARR and flying one of the lines could be heard. They cleaned out the radar reflectors, then set about collecting snow data. The corner reflectors are used to assess the airborne radar observations.

Ludo measured snow density and temperature, as well as snow stratigraphy and grain size information.

This early in the season, snow under the tree canopy is markedly lower than elsewhere on the Mesa.  Not much movement of snow occurs early in the season as long as vegetation holds it.  Much of the snow here remains in the canopy above, which will drop, melt, and sublimate over coming weeks.

Chris used a magnaprobe, an automated snow depth measurement device that records snow depth and GPS-location into a backpack mounted datalogger.


In all, five snow pits were performed and over 1500 snow depths were measured at various points along several pre-determined flight lines.

Colorado’s Grand Mesa is a high elevation surface covered in shrubland, meadows, and trees. Three SWESARR flight lines were distributed over the Mesa and ground observations and travel are indicated. Trees (inset) have a pronounced impact on snow depths, with snow depths low directly under the canopy and much higher adjacent to tree canopy.


After a week of snowfall, welcome clear and calm conditions resulted in an outstanding day collecting ground-truth data useful for assessing instruments and algorithms for the early-season snowpack.

Snow, wind, trees, and topography interact to determine snow depths on Grand Mesa. Fog rolls onto the west end of the Mesa.

Leave a Reply

Keep comments relevant. Inappropriate or offensive comments may be edited and/or deleted. Avoid adding Web site urls.