Science ReportGregory Leonard
Finally today I had the opportunity to initiate my surface investigation on an extended morning EVA. My study is evaluating visible to near infrared (VNIR) spectroradiometric fidelity between in-situ, sunlit rock and soils with the same target materials brought back to the Hab and measured under calibrated artificial illumination. Averaged field spectra will also be used to calibrate / validate 1) an Earth Observatory-1 Hyperion hyperspectral image acquired over MDRS site, and 2) possibly an Advanced Spaceborne Thermal Emission and Spectroradiometer (ASTER) multispectral image that I’ve requested from NASA to be acquired during our MDRS-144 mission period. This was a productive and educational EVA: 17 of 28 primary field VNIR measurements and associated samples were acquired and returned to the lab (see Science Report). Calibration / validation work is essential for expanding the range of accurate aerial platform and space-based sensor mapping and monitoring. This will be the case at FMARS (and also Mars) for more confident selection of study sites, and to complete interpretations and analyses of areas where field access is limited or not-possible.
The sample survey grid is 60 x 120 meters in size and located 300 meters south of the Hab; it is bisected by Cow Dung Road. The grid contains 28 sites positioned on 20 meter centers established in 4 rows (A to D, north to south) by 7 columns (1 to 7, east to west). Survey equipment was first set-up in northeast corner of grid (site A7). Navigation was controlled by pre-selected GPS waypoints guided by variable reflectance responses as observed on multispectral and hyperspectral imagery. At all stations, several site parameters were recorded (e.g. sky conditions, site slope/aspect, sensor – target distance, sun – target phase angle and pointing direction, description of target material). Systematic VNIR spectroradiometric measurements of in-situ rock and soil were collected by an ASD HH Field VNIR Spectroradiometer, preceded in most cases by dark current and white panel reference calibration readings. The constant diffuse skylight today, as a result of cloud cover, was actually very welcome conditions for collecting VNIR spectra (reduced specular reflectance). Rock and soil samples of spectra targets were collected in pre-labeled cloth bags; samples are approximately 0.5 kg each. 17 of 28 primary sites were completed before returning again by foot to the Hab.
As observed on satellite and aerial imagery the survey grid indeed contained at least four field –differentiable units; this is perfect for the study. The eastern portion of the grid was predominantly composed of sub- east/west trending ridge-like outcrops of flat-dipping fine grained buff to light green sandstones, interrupted by in-filled hollows of alluvial, and likely wind-blown, very fine, unconsolidated sand and silts. The western portion of the grid contained a domical hill composed of a strongly oxidized red-brown layer of siltstone/mudstone. Strong in-situ weathering of this unit produced a centimetric scale mudcrack veneer. A large part of the western half grid is covered by silt through pebble sized alluvium and windblown sediments. A fourth unit of white siltstone will be investigated on the next EVA.
In-Hab preliminary inspection of individual unit spectra indicates that there is sufficient spectral variability and seperability between unit types to form a basis for spectral angle mapping analysis. Field measurements and sampling must be completed for remaining sites, in addition to in-Hab lab spectral collection.