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Dr David Hooper

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Instrument Support Level

Manufacturer & Model

Campbell Scientific 107 thermistor, Vaisala HMP45C , Environmental Measurements ARG100, Kipp and Zonen CM3

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Campbell Scientific Surface Meteorological Sensors

A Campbell Scientific (CR10) data logger is used to record surface meteorological data from a number of sensors at the National Centre for Atmospheric Science (NCAS) Capel Dewi Atmospheric Observatory (CDAO). The following data products are available at 10 minute intervals:

  • Air temperature
  • Relative humidity
  • Rainfall
  • Downwelling shortwave radiation

Instrument Details
  • Latitude: 52.425068°N
  • Longitude: -4.0047169°E
  • British National Grid Reference: SN6378382678
  • Altitude above mean sea level (base of instrument): 55 m
  • Height of sensors above ground: 1 m (except for the tipping bucket raingauge, which is at ground level)
  • Notes: this instrument is operated in support of NCAS’s long term measurement programme. It is not bookable.

Summary of Dataset

The sensors are initially sampled at 5 s intervals before representative values (mostly means) are calculated for 10 minute intervals. Only the latter are available.

Air Temperature

  • Sensor: Campbell Scientific 107 thermistor temperature probe mounted inside a URS1 unaspirated radiation shield
  • Accuracy: +/- 0.4 °C
  • Data products: minimum, mean, and maximum values for 10 minute sampling period. Note that the minimum and maximum values represent 1 minute mean values within the 10 minute sampling period.

Relative Humidity

  • Vaisala HMP45C temperature and relative humidity probe (from which only the humidity measurements are used) mounted inside an URS1 unaspirated radiation shield.
  • Accuracy: +/- 0.3%
  • Data products: mean value for 10 minute sampling period

Rainfall

  • Sensor: Environmental Measurements) ARG100 tipping bucket rain gauge
  • Accuracy: typically 99% (according to the manufacturer)
  • Data products: rainfall accumulated within each 10 minute period
  • Notes: The tipping bucket is designed to detect accumulations of 0.2 mm of rain. This means that precipitation events characterised by rates of less than 1.2 mm/hour will not appear to be continuous. Moreover, the rain gauge will not detect precipitation events that lead to a total accumulation of less than 0.2 mm of rain. Occasionally the rain gauge will detect a single tip in the morning as the result of overnight condensation or frost that subsequently melts. The rain gauge will occasionally fail to detect rain as a result of the inlet becoming blocked (e.g. with airborne seeds, leaves, or the build-up of slime) or of the tipping mechanism becoming obstructed (e.g. by an ants’ nest or snails). The instrument is subject to a maintenance schedule in order to avoid such problems).

The data are currently only available in NASA Ames (ASCII) format files using a File Format Index of 1001. Refer to Gaines and Hipskind (1998) for a full description of the file format. Here I will just describe the bare minimum that you need to know in order to read in the data. I’m using the convention that the first line/value number is 1 rather than 0. Where multiple values are given on a single line, they are separated by white space(s).

  • Line 1: two values. The first gives the number of (metadata-containing) header lines, nr_header_lines). The second gives the File Format Index, whose value is always 1001.
  • Line 7: six values. These give the date (UTC) for which data are available followed by the date on which the file was created, both in YYYY MM DD format. the date (UTC) for which data are available and the date on which the file was created.
  • Line 12: ten values specifying the missing datum values for the primary variables, i.e. for all of the variables except the first one, which records the the sample time. Note that there are occasional gaps in the data and so it is important to check for occurrences of missing datum values.
  • Lines (nr_header_lines + 1) to (nr_header_lines + 145): contain 11 values:
    • Value 1: start time of 10 minute sampling period given as the number of seconds past 00:00:00 UTC for the day in question
    • Value 2: Minimum air temperature within the 10 minute sample period (°C)
    • Value 3: Mean air temperature within the 10 minute sample period (°C)
    • Value 4: Maximum air temperature within the 10 minute sample period (°C)
    • Value 5: Mean air pressure within the 10 minute sample period (hPa)
    • Value 6: Mean relative humidity within the 10 minute sample period
    • Value 7: Accumulated rainfall within the 10 minute sample period (mm)
    • Value 8: Integrated downwelling shortwave flux within the 10 minute sample period (kJ m-2)
    • Value 9: Estimated duration of sunshine within the 10 minute sample period (hours)
    • Value 10: Data logger battery voltage at the end of the 10 minute sample period (V)
    • Value 11: Data logger internal temperature at the end of the 10 minute sample period (°C)

You will need to have a CEDA account in order to be able to download files from the data archive.