In-ice irradiance

Vertical profiles of downwelling spectral irradiance were periodically made in boreholes drilled in melting white ice and melt ponds during July-September. A small, downward-looking optical sensor, attached with a plastic optical fiber to an SE-590 spectrophotometer on the surface, was used to view a highly reflective, upward-looking, diffusely reflecting disk. On several occassions the ASD Ice-1 spectroradiometer was used to measure the upwelling irradiance. Boreholes were cut using either a 2 in. CRREL auger or a 6 in. Finnbore auger. Two spectrophotometers with separate wavelength calibrations were used for the measurements. One monitored light sampled by the profiler, while the other (designated as the 'reference') monitored any changes in the incoming light field with a cosine collector approximately 3 m from the borehole. Usually, profiler scans were taken first at the deepest point in the ice and then brought up towards the surface in 20-cm increments. Reference scans were normally taken for each profiler scan. On days when the incident light field was relatively constant, fewer reference scans were taken. In general, light levels decreased progressively with depth. However, late in the summer, light levels occasionally increased with depth in white ice boreholes due to light received from nearby melt ponds. The data can thus, can reflect both vertical and horizontal variations within the ice.

July 6: White ice and melt pond profiles were measured about 15 m SE of CRREL hut. The white ice was 1.85 m thick, while the melt pond was 20 cm deep over 1.83 m of ice. Measurements were made under partial overcast with the solar disk plainly visible.

July 9: The experimental area was located at the same site as the July 6 measurements. Melt pond depth had increased to 24 cm. The white ice was covered by an 8-cm-thick drained layer. Measurements were made under a cirrus/altocumulous cloud deck and highly variable incident light conditions.

July 14: The measurements were made in a particulate-laden hummock field south of station Tuk, and adjacent to a large area of clean white ice. Profiles were made in a 6-in.-diameter Finnbore hole. There was complete overcast, and the solar disk was barely visible.

July 27: Measurements were made just south of the CRREL hut in white ice and melt ponds. Melt ponds were present on three sides of the white ice site, about 2-5 m away from the profile hole. White ice thickness was 1.68 m. The melt pond depth was 34 cm at the hole, with 1.46 m of ice below.

August 6: Measurements were made in white ice and a medium blue melt pond just SE of the CRREL hut, concurrently with optical profiles made by S. Pegau. White ice depth was 1.55 m; the melt pond was 38 cm deep and covered ice 65 cm that was in thickness. Holes were cut with the 6 in. Finnbore. There was complete overcast, and the solar disk was not visible.

August 14: Measurements made in two holes at a sediment-laden site in a ridge east of PAM station Florida. There was complete overcast, and the solar disk was not visible. Ice thickness was 2 m.

August 15: Two profiles were taken in white ice in a first-year, remote ice floe. Ice thickness was 1 m. There was complete overcast, and the solar disk was not visible.

August 19: Measurements were made near the CRREL hut on an ice-covered melt pond and an adjacent hummock. White ice thickness was 1.64 m with a trace of new snow. The melt pond had 2 cm of new ice, 41 cm of water, and covered ice that was 74 cm thick. There was complete overcast, and the solar disk was barely visible.

August 23: Site was located near an azure-blue melt pond on the flank of an old pressure ridge and an adjacent white ice hummock. The frozen surface of the melt pond was cleared of snow for a 1.40 m radius. There was 4 cm new ice on the pond, overlying 37 cm of water. The ice thickness was greater than 1.5 m. Measurements were also made beneath the nearby hummock whose thickness was greater than 2 m and covered by 0.5 cm of new snow. It was snowing, with complete overcast, and the solar disk was not visible.

August 26: The site was located about 5 m south of the CRREL hut. This was an experiment to measure light profiles in hummocks and melt ponds of different sizes and, also, to observe the effect of surrounding melt ponds on light levels beneath a hummock. Ice thicknesses were 1.0 and 1.65 for the small and large hummocks, respectively. The small melt pond had a 11 cm layer of ice at the surface, 33 cm of water, and 85 cm of underlying ice; the large melt pond had 7 cm of ice on the surface, 31 cm of water, and 54 cm of ice. The sky was completely overcast, and the solar disk was not visible.

September 3: Profiles were taken beneath a melt pond and hummock near station Pittsburgh. The melt pond had a trace of new snow, a 13-cm layer of ice, 36 cm of water underlain by 59 cm of ice. The white ice hummock had 2 cm new snow and was 143 cm thick. There was a complete overcast, and the solar disk was not visible.

Albedo  Wavelength-integrated albedo  Spectral albedos   Transmittance

Home

Optics

Mass

Snow

Aerial

Logs