TY - Generic T1 - Measurement of the bidirectional reflectance of snow at fine spectral and angular resolutions T2 - 70th Annual Western Snow Conference Y1 - 2002 A1 - T H Painter A1 - Dozier, J. KW - Bidirectional reflectance factor, Solar zenith angle, Snow texture, Backscattering AB - This paper presents measurements of the bidirectional reflectance factor (BRF) of snow made at finespectral and angular resolution with the Automated Spectro-Goniometer (ASG) for a range of solar zenith angles(0o = 40-50deg) and snow textures (surface grain size = 80 - 240 /an) on two days. Measurements of the stratigraphyof snow texture and density accompanied each day's suite of measurements. The BRF for fine grain, faceted snowexhibited a local backscattering peak at the view zenith near the solar zenith angle, whereas those for mediumgrain, clustered snow did not have a local backscattering peak. The BRF decreased at all wavelengths for anincrease in measured grain radius from 80 /mi to 240 /mi. However, the decrease in BRF in the visible wavelengthswas strongest at Or = 80deg in the forward direction and strongest for A > 1.8 /mi near Or = 30deg in the backwarddirection. As solar zenith angle decreased from 47deg to 41deg the BRF increased near nadir for A < 1.03 /mi but decreased with coherent angular structure for A > 1.03 /mi. JF - 70th Annual Western Snow Conference T3 - Proceedings of the 70th Annual Western Snow Conference PB - Western Snow Conference CY - Granby, Colorado UR - sites/westernsnowconference.org/PDFs/2002Painter.pdf ER - TY - Generic T1 - MAPPING SNOW ALGAE CONCENTRATIONS IN THE SIERRA NEVADA WITH IMAGING SPECTROSCOPY T2 - 69th Annual Western Snow Conference Y1 - 2001 A1 - T H Painter A1 - Duval, B. A1 - Thomas, W.H. A1 - Mendez, M. A1 - Heintzleman, S. A1 - Dozier, J. KW - Simulation modeling, Snow algae AB -

We present spectral reflectance measurements of algal snow and a model to retrieve snow algal concentration from imaging spectrometer data collected in the Tioga Pass region of the Sierra Nevada, California. Spectral reflectance measurements of snow containing the algae Chlamydomonas Nivalas exhibit carotenoid absorption in the wavelength range 0.4 — 0.58 pm and chlorophyll—a,-b absorption in the wavelength range 0.6 — 0.7 pm. The integral of the scaled chlorophyll-a,-b absorption feature, 1680, varies with algal concentration, Ca. The relationship appears to be exponential but this model is not yet statistically significant due to limited data at high concentrations. Using the relationship, Ca = 922.61 exp(13.56 Isub680), we inverted Airborne Visible Imaging Spectrometer (AVIRIS) data for algae concentration. In the 5.5 km , imaged region, the mean algal concentration was 880 cells/mL with a standard deviation of 1445 cells/mL. We calculated the total imaged algal biomass, Ba = 11.1 kg. From the field spectral measurements, we fit a model relating snow albedo, AsubS, to Ca. We inverted algae concentration images for albedo using this model. Mean retrieved albedo was 0.595 with a standard deviation of 0.009, a minimum of 0.43, and a maximum of 0.62.

JF - 69th Annual Western Snow Conference T3 - Proceedings of the 69th Annual Western Snow Conference PB - Western Snow Conference CY - Sun Valley, Idaho UR - sites/westernsnowconference.org/PDFs/2001Painter.pdf ER - TY - Generic T1 - Automated spectro-goniometer: A robitic arm for the measurement of snow bi-directional reflectance distribution function T2 - 68th Annual Western Snow Conference Y1 - 2000 A1 - T H Painter A1 - Paden, B.E. A1 - Dozier, J. KW - Instrumentation, Snow measurements, Snow properties AB - We describe the UCSB Automated Spectro-Goniometer (ASG), a two-axis robotic arm paired with a field spectroradiometer for the rapid and accurate measurement of the optical bi-directional reflectance distribution function (BRDF) of snow. Improvements in radiative transfer models and remote sensing algorithms for snow properties require a more accurate characterization of the angular distribution of reflectance of snow. Previous measurements of snow BRDF have been incomplete with respect to one or more of spectral range, spectral resolution, angular resolution and sampling, solar zenith sampling, and snow characterization. The kinematics of the ASG may be described by Rodrigues ' fonnula for a 2 degree of freedom arm. We describe the forward kinematics for the ASG and then solve the inverse problem from given view angle to necessary rotation about each axis. Its two-dimensional hemispheric sampling space facilitates the measurement of spectral reflectance from snow into any direction. The ASG will usually sample a 10deg hemispheric grid at a 0.5 Hz sampling rate. We will also sample the solar principal plane at 1deg angular resolution at 0.5 Hz sampling rate. With a total weight of 41 kg, the ASG is easily portable by an individual via sled. JF - 68th Annual Western Snow Conference T3 - Proceedings of the 68th Annual Western Snow Conference PB - Western Snow Conference CY - Port Angeles, Washington UR - sites/westernsnowconference.org/PDFs/2000Painter.pdf ER -