Water temperatures based on TR-chain data in a small shallow Lake Vendyurskoe in Russia during 27 March-6 April 2020

The measurements were carried out 27 March–6 April 2020 on small ice-covered shallow Lake Vendyurskoe (62.215784N, 33.262784E, North-Western of Russia). Surface area of the lake is 10.4 km2, its mean and maximal depths are 5.3 and 13.4 m. The maximal length of the lake is 7 km; and the average width is 1.5 km. The mooring equipment was deployed on the ice 350 m from the northern shore, with a location depth of ~ 7 m. The measuring complex included a pyranometer placed directly under the ice to measure downwelling irradiance (a M-80m universal pyranometer, produced in Russia, accuracy 1 W m-2, sampling frequency one minute), two Star-shaped pyranometers (Theodor Friderich & Co, Meteorologishe Gerate und Systeme, Germany, accuracy 0.2 W/m2, sampling interval one minute) placed at one meter above ice surface to measure downwelling and upwelling irradiance, thermistor chain (13 temperature sensors TR-1060 RBR, Canada, accuracy ±0.002°C, resolution ±0.00005°C, sampling frequency 10 s; sensors were placed at intervals of 0.5 m, starting from 0.2 m from the ice bottom to a depth of 6.2 m), and two ADCPs (2 MHz HR Aquadopp current velocity profiler, Nortek AS, Norway). The two ADCPs were mounted on a special retaining frame that rigidly fixed the instruments on the ice and to each other. Both devices were installed in a hole with emitters located 3 cm below the lower ice boundary. For the entire measurement period, the devices were set up as follows: signal discreteness was one minute (32 pulses with a frequency of 2 Hz), depth scanning range was 2.875 m (115 cells with a size of 25 mm). To exclude the mutual influence of the two ADCPs, the emitters were set in an asynchronous mode with a 30 s delay. In the first stage of experiment – from 17:00 LT (local time = UTC + 3 h) on 27 March 2020 to 09:30 LT on 30 March 2020 – the ADCPs emitters were located at a distance of 1.5 m from each other, and at a depth of 1.61 m one beam from each of the devices intersected. In the second stage – from 10:00 LT on 30 March 2020 to 10:00 LT on 6 April 2020 – the distance between the emitters was 0.75 m and two pairs of beams intersected at the same depth