In:
Geoscientific Instrumentation, Methods and Data Systems, Copernicus GmbH, Vol. 7, No. 2 ( 2018-06-18), p. 169-178
Abstract:
Abstract. This study presents a new instrument called a low-cost albedometer (LCA)
composed of two illuminance sensors that are used to measure in situ
incident and reflected illuminance values on a daily timescale. The ratio
between reflected vs. incident illuminances is called the albedo index and can be compared with actual albedo values. Due to the shape of the
sensor, the direct radiation for zenith angles ranging from 55 to 90∘
is not measured. The spectral response of the LCA varies with the solar
irradiance wavelengths within the range 0.26 to 1.195 µm, and the
LCA detects 85 % of the total spectral solar irradiance for clear sky
conditions. We first consider the theoretical results obtained for 10
different ice and snow surfaces with clear sky and cloudy sky incident solar
irradiance that show that the LCA spectral response may be responsible for an
overestimation of the theoretical albedo values by roughly 9 % at most.
Then, the LCA values are compared with two “traditional” albedometers, which are CM3
pyranometers (Kipp & Zonen), in the shortwave
domain from 0.305 to 2.800 µm over a 1-year measurement period
(2013) for two sites in a tropical mountainous catchment in Bolivia. One site
is located on the Zongo Glacier (i.e., snow and ice surfaces) and the second
one is found on the crest of the lateral moraine (bare soil and snow
surfaces), which present a horizontal surface and a sky view factor of 0.98.
The results, at daily time steps (256 days), given by the LCA are in good
agreement with the classic albedo measurements taken with pyranometers with
R2=0.83 (RMSD = 0.10) and R2=0.92 (RMSD = 0.08) for the
Zongo Glacier and the right-hand side lateral moraine, respectively. This
demonstrates that our system performs well and thus provides relevant
opportunities to document spatiotemporal changes in the surface albedo from
direct observations at the scale of an entire catchment at a low cost.
Finally, during the period from September 2015 to June 2016, direct
observations were collected with 15 LCAs on the Zongo Glacier and
successfully compared with LANDSAT images showing the surface conditions of
the glacier (i.e., snow or ice). This comparison illustrates the
efficiency of this system to monitor the daily time step changes in the
snow and ice coverage distributed on the glacier. Despite the limits imposed by
the angle view restrictions, the LCA can be used between 45∘ N and
45∘ S during the ablation season (spring and summer) when the melt
rate related to the albedo is the most important.
Type of Medium:
Online Resource
ISSN:
2193-0864
DOI:
10.5194/gi-7-169-2018
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2018
detail.hit.zdb_id:
2690575-9
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