EX-7
Cold Land Processes Mission
Airborne/Field Experiment
Spring, 2002


Draft Experiment Plan
November 18, 1999



 

Overview

The fundamental purpose of the EX-7 Field Experiment is to provide ground, airborne, and satellite data sets necessary to achieve mission objectives specified in the Irvine Report. Additionally, the experiment should foster a broad spectrum of science investigations both during the experimental period and afterwards.

At the most fundamental level, the EX-7 Field Experiment has but one goal. It must provide data sets that are required to develop, refine, test, and finalize microwave remote sensing retrieval algorithms in preparation of a mission-ready proposal for the Cold Land Processes Mission.

To support the specific EX-7 mission planning objectives, the field experiment must:

  1. Provide "ground truth" for snow characteristics and freeze/thaw characteristics, necessary to develop, refine, and test remote sensing retrieval algorithms.
  2. Provide microwave (active and passive) and optical remote sensing data from various ground, airborne, and satellite platforms.

Ground truth is expected to be comprised of at least three levels of information.

  1. There must be an attempt to identify and intensively measure locations that a) have desired characteristics, such as deep snow, shallow snow, boggy soils, dense forests, etc, and b) can be considered a pure pixel and unambiguous from the remote sensing point of view. These sites will serve as Level 1 Ground Truth. These sites will ultimately provide the highest degree of confidence in the algorithms, however there will be relatively few of these sites due to the intensive resources required to measure them.
  2. There must be an attempt to characterize surface conditions on a larger scale than "pure pixels". Here, an appropriate sampling scheme is required to observe properties over larger areas, such as complete flight lines. The objectives at this Level 2 Ground Truth scale are to take full advantage of the airborne data, to try to better understand how remote sensing data relates to changing surface conditions, etc.
  3. Finally, there must be an attempt to characterize surface conditions over very large areas. This requires spatial modeling, and therefore cannot truly be considered "truth". However, model response will provide insight into physical characteristics affecting remote sensing signals, such as snow wetness, soil temperatures, etc., that simply cannot be measured over sufficiently large areas. This Level 3 Ground Truth is intended more for diagnosis of remote sensing data and signal behavior than for validation purposes.

The EX-7 Field Experiment will generate a rich data set that will be useful for broader scientific objectives. For example, the Level 3 modeling component will necessarily involve combining atmospheric models with detailed land surface schemes, and will provide important land surface information during a complex transitional period. The potential benefits of the mission to atmospheric science are obvious. The incorporation of broader science objectives in the experiment is critical, and should be encouraged. However, other objectives must be carefully assessed in order to ensure that they do not detract from the basic mission planning objectives defined above.

Selection of an appropriate study site is critical to the success of the field experiment. Four sites were initially suggested: Alaska, the Sierra Nevada, the Rocky Mountains, and Minnesota. Each suggested site has pros and cons associated with it; no site has everything that might be desired for a field campaign.

After careful consideration, one site is proposed for the EX-7 Field Experiment. The important criteria for site selection were:

Proposed Study Area

The full study area proposed for the EX-7 Field Experiment is located in north central Colorado (Figure 1). The full study area is 3ox5o (104o - 109oW, 38o-41oN). At  39.5oN, the study area is 430 km (267 mi) across. It  is 333 km (207 mi) N-S. In considering this area for the EX-7


Figure 1. The State of Colorado, and the proposed location of EX-7 Field Experiment.
 


Field Experiment, several important strengths were recognized:


 Within the full study area are six proposed Intensive Study Areas (ISAs), where intensive ground truth data will be collected:

  1. North Park (Vicinity of Walden, CO, 25 miles NE of Steamboat Springs, CO)
  2. Rabbit Ears Pass (10 miles SE of Steamboat Springs, CO)
  3. Fraser Experimental Forest (30 miles west of Boulder, CO)
  4. Niwot Ridge (20 miles west of Boulder, CO)
  5. Grand Mesa (20 miles E of Grand Junction, CO)
  6. Upper Gunnison River Basin

Each of these ISAs have unique characteristics that together ensure that a wide range of snow and freeze/thaw characteristics can be sampled, with low risk of weather-related failure (e.g. lack of snow or freeze/thaw transitions).

Opportunistic Study Areas (OSAs) may also be possible. These would be areas that often have snow or frozen conditions, but not reliably enough to devote the level of resources required for an ISA. In the event of favorable conditions, ground teams and aircraft could be directed to a pre-determined OSAs to extend the range of physiographic conditions observed.
 

Study Area Characteristics

The study area is most frequently characterized by its rugged mountain topography and deep mountain snow packs, but in fact it contains many different physiographic, climatic, hydrologic, and ecologic characteristics. Steep elevation gradients result in rapid changes in characteristics over short distances. The resulting diversity is beneficial to meeting the objectives of the field experiment, which require a wide range of snow and freeze/thaw conditions to fully evaluate algorithms. Colorado is basically arid; deep seasonal snow packs are primarily limited to the highest elevations. Much of the study area is more likely to have relatively shallow snow packs, on the order of a 1'-2' or less. On the high elevation open parklands, snow packs tend to be relatively shallow and windswept, with enhanced nighttime radiative cooling resulting in significant freezing conditions. For example, Fraser CO is frequently dubbed the "ice box of the nation" for it's extreme cold temperatures (Table 1).


Table 1. Monthly Climatic Data for FRASER for years 1990 - 1997
Station - 53116   Latitude - 3952   Longitude - 10545   Elevation - 8575

             Jan     Feb     Mar     Apr     May     Jun     Jul     Aug     Sep     Oct     Nov     Dec  Annual

Monthly mean temperature.
Ave         12.5    16.4    24.6    32.7    43.8    51.2    54.7    54.2    46.7    36.1    21.2    11.8    33.5

Monthly mean maximum temperature.
Ave         28.2    33.2    39.9    47.4    61.1    71.0    74.9    74.1    65.5    53.6    35.6    28.5    50.9

Monthly mean minimum temperature.
Ave         -3.2    -0.7     9.3    18.1    26.4    31.3    34.4    34.2    28.0    18.6     6.8    -4.8    16.4

Number of days with min. temp. <= 0 deg.F.
Ave         17.4    14.2     5.6     0.7     0.0     0.0     0.0     0.0     0.0     1.0     8.7    21.4    75.0

Number of days with min. temp. <= 32 deg.F.
Ave         31.0    28.2    30.9    29.3    27.5    18.5    12.1    12.0    21.8    30.6    29.8    31.0   325.0

Total monthly precipitation.
Ave         1.78    1.76    2.01    2.38    1.76    1.22    1.26    1.32    1.35    1.03    1.67    1.59   19.64

Total monthly snowfall.
Ave         29.4    26.2    25.7    18.7     2.5     0.7     0.0     0.0     1.6     8.3    21.2    25.1   163.5

Number of days with snowdepth >= 1 inches.
Ave         31.0    28.2    27.5    19.8     1.2     0.1     0.0     0.0     0.5     6.0    23.2    31.0     0.0



 

Land Cover and Hydrography

The study area consists of three major land cover regimes distributed east-west across the area: 1) prairie grasslands and croplands in the eastern fourth of the area, 2) desert and high-altitude plateaus in the western fourth, and 3) a mixture of forested mountains and valleys, and alpine areas in the middle two-fourths of the area (Map 1). Two large, open parklands lie within the mountainous part of the study area: North Park, surrounding Walden, CO, and South Park, southeast of Leadville, CO. Both areas are broad, open, rolling grasslands at high elevation (North Park lies at ~8000', South Park at ~9000').

The study area contains the headwaters for seven major river systems: 1) North Platte R., 2) South Platte R., 3) Arkansas R., 4) Yampa R., 5) White R., 6) Gunnison R., and 7) Colorado River. The study area is finely dissected by these river systems. The total downstream water yield from these basins is directly proportional to the mountain snow pack.
 

Forest Cover

Forest cover types within the study area are predominantly Spruce-Fir, Lodgepole Pine, Ponderosa Pine, Pinyon-Juniper, and Chaparral (Map 2). About one-third of the study area is unforested. Forest cover density generally increases with elevation to the local tree-line (Map 3).
 

Soils

Surface soils (upper 5 cm) in the study area are predominantly sandy loam or loam (Map 4). Clay soils are prevalent in the Colorado Piedmont area (i.e. the Denver/Boulder area) and along parts of the Colorado River. Sandy soils are found in the northeast (e.g. South Platte valley) and northwest parts of the study area (e.g. western Yampa valley). The bulk density of surface soils is shown in Map 5.
 

Precipitation/Climate

Most of this region's annual precipitation occurs as winter snowfall (Map 6). Pacific frontal systems bring most of the winter moisture to this region. These storm systems can arrive into the region from either the west, northwest, or southwest, and this influences the distribution of precipitation. Westerly tracks are orographically uplifted to some extent by the Wasatch Plateau east of the study area in Utah, and are lifted further by the ranges along the Continental Divide in the central part of the study area. This results in the heaviest precipitation west of the Continental Divide. Northwesterly tracks are lifted by the Wasatch Range and the Uinta Mountains in Utah and by ranges along the divide in the north central part of the study area, resulting in heavier precipitation at these locations. Storm tracks arriving from the southwest don't encounter major orographic effects until they reach the San Juan Mountains in southwestern Colorado, just south of the study area (i.e. south of the Gunnison River in Figure 1). Heavy winter precipitation occurs in this part of the region from these storm tracks. In general precipitation declines markedly throughout areas east of the Continental Divide. However, low pressure systems east of the Divide can bring significant moisture in from the Gulf of Mexico during Spring, resulting in sometimes heavy snow fall in the foothills at lower elevations on the eastern side of the Divide. Lower elevation areas of the Central Rockies receive considerably less precipitation; most of the region's snow pack storage is concentrated in the higher mountains.

The mean date of snow cover formation ranges from October 15 near the Continental Divide to November 15 for most of the rest of the study area. The mean date of snow cover disappearance ranges from early March in the western part of the study area to May 1 in all but the highest elevations near the Continental Divide.
 

Snow Measurement Networks

There are three large-scale snow measurement and monitoring networks within the study area (Map 7): 1) SNOTELs, 2) Snow Courses, and 3) Airborne Gamma surveys.

The National Resource Conservation Service (NRCS) operates over 50 automated SNOw TELemetry sites within the study area. These sites monitor snow water equivalent (SWE) on either an hourly or daily basis using a pressure-sensing pillow. Data are telemeterd using meteor-burst technology to a central processing facility in Portland, OR. Data are generally available a few hours after they are collected. The NRCS has plans to augment SNOTEL sites with soil temperature profile measurements, but has limited resources to do so. It may be possible to collaborate with them to install appropriate sensors within the study area during the summer prior to the field experiment, if desired.

The NRCS also operates 60-70 manual snow courses within the study area. These are transects of varying lengths that are generally measured once a month during the winter and spring. Not all of the NRCS snow course sites may be active, and many are co-located with SNOTEL sites. In many cases snow course records go back several decades. It may be possible to arrange for more frequent data collection on some courses than just once a month, if desired.

The National Operational Hydrologic Remote Sensing Center, of the National Weather Service, maintains about 40 airborne gamma survey flight lines within the study area. SWE is determined by measuring the attenuation of terrestrial gamma radiation due to the water content of the snow. Depending on the method of data processing, the SWE measurement is either an average for the flight line area (typically about 3000 m wide by 10 km long), or a series of SWE measurements along the flight line. See http://www.nohrsc.nws.gov/98/html/gamma/gammapage.html for more infomation. Additional flight lines can be added for the field experiment, but this must be done the previous fall in order to collect background gamma radiation measurements.

Transportation

Colorado's transportation network is generally very good (Map 8). Major interstates traverse the study area from east to west (I-70) and from north to south (I-25). There is a relatively dense network of primary and secondary roads that span the study area. These roads are generally well-maintained throughout the winter and spring. Storm conditions or severe blowing snow conditions may temporarilly prevent study area access via major roads. Access to areas away from roads shown on the map may require snow machines, skis, or snowshoes. Cooperative ski areas may provide ready access to backcountry areas that otherwise would be difficult or time-consuming to access.

There are numerous airports throughout the study area that provide aircraft maintenance and fuel for light aircraft. Several airports support larger jet aircraft, including Denver, Colorado Springs, Hayden, and Grand Junction. Major air carrier service is available to these locations, facilitating investigator access to the study area. Airports within or near the study area that are capable of handling the NASA DC-8 aircraft (considering runway structure, aircraft gross weight and landing gear, and fire and rescue facilities) are limited to Denver International Airport, Colorado Springs Municipal Airport, and Salt Lake City International Airport.
 

Intensive Study Areas

Six  ISAs are proposed. The first five are relatively small areas, each with unique physiographic characteristics. Collectively, these areas will provide a broad range of snow and freeze/thaw conditions; intensive ground data collected from these areas will be used  to develop and test remote sensing retrieval algorithms. The sixth ISA is a large basin (~50,000 km2) that itself contains a similarly broad range of conditions. Intensive ground data will be collected from this area also, but withheld from algorithm development, for the purpose of an independent validation of the algorithms that result from the experiment.

  1. North Park (Vicinity of Walden, CO, 25 miles NE of Steamboat Springs, CO)
  2. Rabbit Ears Pass (10 miles SE of Steamboat Springs, CO)
  3. Fraser Experimental Forest (30 miles west of Boulder, CO)
  4. Niwot Ridge (20 miles west of Boulder, CO)
  5. Grand Mesa (20 miles E of Grand Junction, CO)
  6. Upper Gunnison RIver Basin

Each of these ISAs have unique characteristics that together ensure that a wide range of snow and freeze/thaw characteristics can be sampled, with low risk of weather-related failure (e.g. lack of snow or freeze/thaw transitions).
 

North Park ISA


The North Park ISA is a broad, high-elevation parkland approximately 25 miles in diameter. The town of Walden, CO is located in the center of North Park. The mean elevation of North Park is about 8100' A.S.L. It is an intermountain glacial basin. The area is surrounded by high mountains that develop deep snow packs, but relatively little snow accumulates in North Park itself (Table 2). This area is the headwaters of the North Platte River. Several small rivers drain the surrounding mountains and flow through the relatively flat topography of North Park, where they join the North Platte just north of Walden. Consequently, the area is relatively wet, and includes the 20,000 acre Arapahoe National Wildlife Refuge, which includes significant wetland areas. North Park is predominantly unforested. Snow packs tend to be relatively shallow and influenced by wind redistribution. Two secondary highways service Walden, providing easy access through the southern half of North Park, and somewhat more restricted access to the northern half. Several smaller roads traverse the area, but these may not be open reliably during winter.


Table 2. Monthly Climatic Data for WALDEN for years 1990 - 1997
Station - 58756   Latitude - 4044   Longitude - 10616   Elevation - 8100

             Jan     Feb     Mar     Apr     May     Jun     Jul     Aug     Sep     Oct     Nov     Dec  Annual

Monthly mean temperature.
Ave         17.9    21.1    29.2    36.0    45.6    54.3    57.8    57.7    50.3    39.1    25.9    18.8    37.8

Total monthly precipitation.
Ave         0.78    0.79    0.62    1.31    1.88    1.26    1.18    0.84    1.66    0.95    0.90    0.51   12.67

Total monthly snowfall.
Ave         10.7     9.5     6.8     8.7     3.4     0.2     0.0     0.0     1.2     6.1    10.3     7.1    64.0



 

Rabbit Ears Pass ISA


The Rabbit Ears Pass area surrounds a 10-mile long section of Hwy. 40 where it crosses the Continental Divide. Although the area is above 9300' A.S.L., the area has low to moderate,  rolling topography, and is predominantly forested. Many open meadows and glades, the relatively gentle topography, and significant winter snow accumulation make this a popular winter recreational area. The area includes a complete micrometeorological station, large lysimeter pans, and a snow course network, supported by the USGS. This was also the site of the WMO intercomparison of winter precipitation gages; the gages are still on the site and are operable. Road access to the area is easy via Hwy. 40, which is well-maintained throughout the winter and spring. Off-road access is also easy, by snow machine or cross-country skiing.

Other science facilities that are nearby include the Storm Peak Laboratory, an atmospheric science facility at the top of Steamboat Ski Area.

Fraser Experimental Forest ISA


The Fraser Experimental Forest is a USDA Forest Service research facility that includes most of the St. Louis Creek basin above Fraser, CO (about 30 air miles west of Boulder, CO, on the west side of the Continental Divide). The area is about 100 km2. The ISA offers a unique opportunity to work on the problem of remote sensing retreivals of snow and freeze/thaw in forested areas. The Fraser Experimental Forest consists of a rich structure of controlled forest characteristics. The forest structure varies from clearcuts (several ha) to patch cuts (< 1 ha) to thinned stands of different age (same species). Chronosequences of lodgepole pine include 50-year (small plots), 75-year (large expanse), and >300-year (large expanse). There are also different structures from cut/leave strips on the Fool Creek watershed, and from different tree densities on north/south slopes. Lexen Creek and Deadhorse watersheds have had stand characteristics extensively mapped and also related to snow course data. Various long-term data sets exist for the site, including extensive weekly snow course information and intensive April 1 surveys since 1964, daily streamflow at 7 sites within the watershed, and a variety of meteorological data.

Facilities at this ISA include on-site housing for up to 28 persons (2 cabins, sleep 3-5 each; lodge, sleeps 6; dormitory, sleeps 12 in individual rooms), cooking facilities, a wet-lab, office, computer space, and a workshop, and 2 snow-cats.

Niwot Ridge ISA


Niwot Ridge is a broad alpine ridge located in the Colorado Front Range, 20 miles west of Boulder, CO. The entire area is above 10,500' A.S.L. The ISA is predominantly alpine tundra, with areas of patterned ground and permafrost. Topography on the ridge itself is mainly low, rolling hills, although terrain drops off steeply on either side of the ridge (Figure X).

Figure. Niwot Ridge is the broad ridge extending from the lower right corner of the photo towards the photo center.
 


Snow distribution is controlled by wind and topography; many areas of the ridge remain snow-free throughout the year as a result. Without insulating snow cover, these areas are susceptible to extreme soil freezing.

The alpine research area of Niwot Ridge, 4 km from the Station, was designated in 1975 as an Experimental Ecological Reserve by the
Institute of Ecology, and in 1979 as a Biosphere Reserve by UNESCO, the U.S. State Department, and U.S. Forest Service. In 1980 Niwot
Ridge was selected by the National Science Foundation as the alpine tundra component of the Long-Term Ecological Research (LTER)
program.

Niwot Ridge has also been the site of extensive atmospheric research. The Mountain Climate Program, initiated by John Marr in 1952,
continues to collect valuable data at five principal sites spanning a 5000 foot altitudinal gradient. The National Oceanic and Atmospheric
Administration has sampled atmospheric gases from Niwot Ridge since 1968. The carbon dioxide record is the third longest in the world, and
is the only long-term record from a continental site.

Niwot ridge is probably the most thoroughly studied alpine area in North America, by virtue of over 60 years of research programs. The
Mountain Research Station is unique in providing these research opportunities within a 45-minute drive of a major university campus

The site is the focus of the Niwot LTER. Many facilities exist to support research on Niwot Ridge, including an alpine laboratory (Figure) with line power and fiber optic telecommunications capabilities, a subnivean laboratory (Figure X) with  complete micrometeorological instrumentation, and a dense network of continuosly monitored soil and snow temperature profiles.

Figure. Alpine laboratory on Niwot Ridge.

The University of Colorado Mountain Research Station (MRS) is an interdisciplinary research facility managed by the University's Institute of Arctic and Alpine Research (INSTAAR), and is located at the base of Niwot Ridge. An unimproved road provides access to the ridge from the MRS. Facilities at the MRS are available to support research activities on Niwot Ridge, including laboratories, lodging, a dining hall, bathhouse and laundry, and meeting rooms. The MRS has two snow cats that can go to Niwot Ridge when snow conditions permit.

Grand Mesa ISA

The Grand Mesa is an 11'000 flat-topped mountain located 20 miles east of Grand Juntion, CO. The area is over 3 million acres. The area is unique for Colorado - the mesa top is relatively flat, and is characterized by forests of Aspen, Engelmann Spruce, and Subalpine Fir, and by nearly 300 lakes and reservoirs fed by melting snow. Wetland areas are extensive. Annual snow accumulation on the mesa is 5-10'. The presence of extensive lakes and wetlands in a forested environment provides a useful surrogate for many boreal areas, such as northern Minnesota.

Year-round access to Grand Mesa is provided by  Hwy. 65 (the Grand Mesa National Scenic Byway). The Mesa is readily accessible by snow machine or skis. There are few facilities on the Mesa itself, but nearby towns below the Mesa summit provide basic facilities, and Grand Junction is less than an hour away.

Upper Gunnison River Basin ISA


The Upper Gunnison River Basin has been the focus of orographic precipitation and distributed hydrologic modeling research for many years, mainly by the USGS Water Resources Division. More recently, this basin has become one of three demonstration basins for the NASA Southwest Regional Earth Science Applications Center (RESAC), with a principal focus on snow cover mapping and snowmelt runoff modeling.

The upper basin is approximately 50,000 km2, and exhibits a broad range of physiographic characteristics. The northern portion of the basin is predominantly montane, while the southern  portion is lower elevation and considerably more dry. Snow accumulation and freezing conditions are reliable throughout much of the basin. Gunnison (e.g. Table 3).



Table 3. Monthly Climatic Data for GUNNISON for years 1990 - 1997
Station - 53662   Latitude - 3833   Longitude - 10655   Elevation - 7630

             Jan     Feb     Mar     Apr     May     Jun     Jul     Aug     Sep     Oct     Nov     Dec  Annual

Monthly mean temperature.
Ave         10.2    17.1    29.9    39.8    48.8    56.8    61.0    61.0    53.2    40.8    26.2    13.2    38.1

Monthly mean maximum temperature.
Ave         26.7    32.4    44.9    55.9    66.3    76.2    79.5    79.4    71.0    60.4    41.0    29.3    54.8

Monthly mean minimum temperature.
Ave         -6.2     1.9    15.0    23.7    31.3    37.3    42.4    42.7    34.1    21.2    11.5    -2.3    21.5

Total monthly precipitation.
Ave         0.82    0.71    0.54    1.11    1.23    0.78    1.19    1.68    1.42    0.73    0.76    0.47   12.39

Total monthly snowfall.
Ave         11.1     7.7     6.3     5.0     0.9     0.0     0.0     0.0     0.0     1.6     5.5     7.1    54.3


The Upper Gunnison Basin ISA provides an opportunity to integrate science results from the EX-7 field experiment into on-going hydrological modeling and forecasting investigations. The area is well suited to serve as an intensive validation site for remote sensing retrieval algorithms developed at the other ISAs.

Access to the area is primarily via Hwy. 50. Several smaller roads provide year-round access throughout most of the basin.
 

Opportunistic Study Areas

In addition to the ISAs described above, there will be opportunities for data collection at other sites. While most of the resources for the experiment will be deployed at the ISAs, an ability to rapidly deploy basic instrumentation and measurement teams at opportunistic sites is desirable. Such sites may include areas such as the high plains in the eastern part of the study area, which do not reliably have snow cover and freezing conditions. If conditions become favorable suring the field experiment, deployment to these sites may be considered. Flexibility in the aircraft schedule is a major factor in this regard.

There are many sites within the study area that may contain substantial instrumentation or relevant measurement infrastructure and could be considered opportunistic study areas. For example, the Shortgrass Steppe LTER east of Fort Collins, CO has many attributes conducive to the field experiment, but only occasionally experiences snow cover and substantial freezing conditions.



End of Draft - 991118