Data Set Overview : A field differential Geopositional Satellite (GPS) survey team which included Jim Garvin, Jack Bufton, Bill Krabill, and Earl B. Frederick deployed a pair of Motorola Eagle II GPS receivers to the southern flanks of the feature known as Mars Hill (an alluvial boulder field superimposed on a major lobe of alluvial and colluvial material in Eastern Death Valley) on Oct. 19, 1989. The objective was to measure the 5-20 cm scale microrelief of the boulder field at pixel scales (30-50 m long transects), with vertical control to the few cm level. These microterrain profiles were to be used to help calibrate radar scattering models, and to compare with helicopter stereo data (FEXP-E-HSTP-4 RDR-TOPOGRAPHIC-PROF-V1.0) for the same location.  The GLOTAS technique, as implemented at the time of GRSFE, involves recording GPS carrier phase data for at least 4 satellites simultaneously with two 8-channel receivers. In this approach, one (master) receiver/antenna is fixed at a reference point (which can be surveyed in using GPS itself), and after a suitable calibration period, the second GPS receiver/antenna system is moved from its position beside the fixed master in whatever pattern is desired to develop a topographic profile or grid. The mobile GPS receiver/antenna permits positional data in all three axes (x,y,z) to be recorded at a rate of once per second, which can then be cross-referenced to the fixed master, and later tied to an absolute geodetic positional reference system. The primary interest was in relative horizontal position and in relative relief at each position. Hence, an inverter was attached to a jeep battery to power a COMPAQ 386 computer to record all the GPS tracking data from both receiver/antenna systems.  Data were collected by cabling the mobile GPS system to the computer by means of a 150 ft. cable, which limited profiling length to just under 50 m.  The system was deployed to the southern flanks of Mars Hill, and a profile position was randomly chosen with a bearing or 040 degrees from true magnetic N (measured from the base of Mars Hill using a Brunton). A 100 m long tape measure was used to demark the measurement positions, which were spaced every 5 cm except for flat inter-boulder regions, at which time measurements were made every 10 or 20 cm (our fractal assumption). The initial profile extended for 37 m on a heading of 040 degrees, and the resampled average measurement spacing was about 10 cm. Measurements were made at 10 sec intervals (10 samples) at each data point, and moved the mobile GPS unit as rapidly as possible between ground sampling points. The antenna was mounted on a fibreglass pole and attached on a circular plate at the top of the 6 ft. long pole to minimize interference due to intervening people etc. The first profile took approximately 50 minutes to collect, and the error analysis suggests that 2-3 cm RMS vertical precision was achieved over the length of a 37 m long GLOTAS profile (we were tracking 6-7 satellites during this operation).  After the success of the initial profile, a second profile position was chosen at random, to extend from the base of the hill to about 30 m distant. The true bearing of this profile was 320 deg. (rel. to magnetic N), and it was chosen so as to begin at the same starting location as Profile 1. Identical conventions were used on this profile, and the average resampled data point spacing was 11 cm. The vertical RMS was again 2-3 cm (max), and if a few of the suspect data points are removed, the vertical RMS precision is as good as 1 cm. This profile required only 35 minutes to collect.  Processing Level Id : 5 Software Flag : N Processing Start Time : 1989-10-20T00:00:00.000 Processing Stop Time : 1990-06-01T00:00:00.000   Parameters :  Data Set Parameter 'PLANETARY RADIUS' ------------------------------------- Radial distance from center of planet or satellite to given location on the surface.  Data Set Parameter Name : PLANETARY RADIUS Data Set Parameter Unit : METER Sampling Parameter Name : ALONG TRACK DISTANCE Sampling Parameter Unit : METER Minimum Sampling Parameter : N/A Maximum Sampling Parameter : N/A Sampling Parameter Resolution : 0.14 Sampling Parameter Interval : 0.05 Minimum Available Sampling Int : N/A Noise Level : 0.03   Source Instrument Parameters : Instrument Host ID : FEXP Data Set Parameter Name : PLANETARY RADIUS Instrument Parameter Name : PLANETARY RADIUS Important Instrument Parameters : 1   Measurement Information : Not Applicable   Processing :  Processing History ------------------ Source Data Set ID : N/A Software : UNK Product Data Set ID : FEXP-E-GPSM-5-RDR-TOPOGRAPHIC-PROF-V1.0

Overview : A detailed statistical analysis was carried out for these data (2 GLOTAS profiles), and height frequency distributions have been derived for detrended versions of the data. In addition, slope frequency distributions were computed at horizontal baselines of 10 cm, 100 cm, 200 cm (to match the average ATLAS footprint scale).