DOI: 10.5285/eb1c141a-6313-43dd-a93c-86bcacd80203
title: Basal probe time-series from sensors installed at the base of boreholes drilled into Khumbu Glacier, Nepal, in 2017 and 2018 as part of EverDrill research project - VERSION 2.0

description: The datasets are basal probe sensor time series measuring suspended sediment concentration, water pressure, electrical conductivity and temperature. Each sensor was located at a discrete depth within one of six boreholes into Khumbu Glacier, Nepal. Boreholes were drilled in May 2017 and 2018 to investigate the internal properties of Khumbu Glacier, specifically ice thickness, temperature, deformation and structure, as part of the NERC-funded 'EverDrill' research project. Supporting borehole information is provided as a related dataset. Funding was provided by the NERC grant NE/P00265X/1 and NE/P002021/1.
description: The datasets are time series of various sensors (suspended sediment content, water pressure, electrical conductivity and temperature) mounted onto a basal probe string, installed in three boreholes drilled into Khumbu Glacier, Nepal. The data are presented in whole or in part in Miles et al. (2018). For borehole information, see the related datasets.
description: Suspended sediment concentration was measured using turbidity sensors based on Orwin & Smart (2004). They use a photo diode to measure the backscatter of infrared light emitted by an infrared light-emitting diode. Water pressure was measured using Omega pressure transducers (model PX209-300GI). They are 4-20 mA current loop transducers that were measured using a 100 Ohm shunt resistor. Electrical conductivity was determined by inverting the resistance measured across two brass-rod electrodes (5 mm diameter, ~11 mm long, 11 mm separation). To cancel polarisation effects, the polarity of the excitation voltage was reversed. Temperatures were acquired by using Honeywell UNI-curve 192-502-LET-AOI negative temperature coefficient thermistors. All sensors were controlled by Campbell Scientific CR1000 data loggers from the glacier surface. Further details are provided in Miles et al. (2018) and Doyle et al. (2018). Resolution: The turbidity (suspended sediment concentration) sensors were calibrated in the laboratory using non-local, fine (grain size &lt; 63 um) glacial sediment, using SSCs ranging from 0 (distilled water) to 6 g l-1. Calibration limitations are detailed in Doyle et al. (2018), but regardless, we expect SSCs between 3 - 20 g l-1 to fall within the full scale range of the sensors. The water pressure transducers are calibrated by the manufacturer, who report the sensors to be accurate to +/- 0.75 psi (+/- 0.53 m head) between 0 - 300 psi. The electrical conductivity sensors were calibrated in sodium chloride solutions against a laboratory EC probe between 0 - 200 uS cm-1. More details are given in Doyle et al. (2018). The thermistors have an interchangeability of 0.4 degrees Celsius. After an ice bath calibration, previous studies have suggested that an accuracy of +/- 0.05 degrees can be achieved around 0 degrees. This is therefore the expected accuracy at 0 degrees, but represents an indication of uncertainty rather than a maximum limit (particularly as temperatures diverge away from 0 degrees). See Doyle et al. (2018) and Miles et al. (2018) for more information.
description: Detailed methodology of suspended sediment concentration, water pressure and electrical conductivity measurements is given in Doyle et al. (2018). Detailed methodology of thermistor measurements, including accuracy estimation, is presented by Miles et al. (2018).