14. URAO¶

14.1. Safety¶

The Observatory should be regarded as a laboratory environment. The same guidelines apply as for other laboratory courses in the Department (see Departmental Handbook).

Note

Do not make adjustments to mains-supplied instruments or attempt to modify any apparatus without consulting either a demonstrator or a technician.
You should not work in the Observatory outside the class contact period, except by special arrangement with a supervising member of staff or a laboratory technician.
On the Observatory, beware of guy ropes attached to masts and overhead instruments. Be especially careful if the ground is muddy. Work in the area you have been shown to work in, as some cables and soil heat flux plates may be near the surface.
Wear suitable, protective footwear (i.e. NOT flip-flops) and beware of low-lying objects which you could trip over. Wear appropriately warm clothes.
Always ask if there are any points which are not clear.

14.2. Instruments¶

14.2.1. Overview¶

Wind

Table 14.1 Wind-related measurements at URAO¶
Instrument	Model	Manufacture	Sampling rate	comment
Ultrasonic anemometer	Windmaster pro	Gill	10 Hz	3 m
propeller anemometer	Gill	Gill	1 Hz	3 m
Wind profile anemometers	A100L2	Vector instruments	1 Hz	2,5, 10 m
Wind vane	W200P	Vector instruments	1 Hz	10 m
Vector Anemometer	A101M	Vector instruments	1 Hz	0.56, 0.8, 1.12, 1.6, 2.24, 3.2, 4.48, 6.4 m

Heat and humidity

Table 14.2 Temperature&humidity-related measurements at URAO¶
Instrument	Model	Manufacture	Sampling rate	comment
temperture probe	DTS12A	Vaisala	1 Hz	in Stevenson screen
Soil temperature	DTS12G	Vaisala	1 Hz	in soil (5cm-10cm-20cm-30cm-50cm-100cm)
humidity probe	HMP45A humidity probe	Vaisala	1 Hz	in Stevenson screen
platinum resistance themometer	PT100/3	Campbell scientific	1 Hz	temp profile (0.56m-1.12m-2.24m-4.48m)
Soil heat flux plate	HEP01	Hukseflux	1 Hz

Radiation

Table 14.3 Radiation-related measurements at URAO¶
Instrument	Model	Manufacture	Sampling rate	comment
pyranometer	CM11	Kipp and zonen	1 Hz	1m
net-radiometer	CNR4	Kipp and zonen	1 Hz	1.3m
Sunshine duration	CSD1	Kipp and zonen	1 Hz	10m

Other

Table 14.4 Other measurements at RUAO¶
Instrument	Model	Manufacture	Sampling rate	comment
infra-red gas analyser	Li-7500RS	Li-Cor	10 Hz	3m
Rain gauge	SBS 500	Environmental measurements Ltd.	1 Hz
Pressure	DPI1 140	Druck	1 Hz
Ceilometer	CL31	Vaisala	3sec row data	processed by R.Brugge 5min data

14.2.2. Eddy Covariance (EC) mast¶

The EC mast at the URAO has a sonic anemometer (Gill R3, Fig. 10.3) which derives the wind-speed from transit times of acoustic pulses travelling in both directions along a fixed path. The wind-speed component along the path is proportional to the difference between the transit times. Three sets of transducer pairs are used to derive the three components of the wind vector u, v, w. In addition, the speed of sound can be deduced:

Also, on the EC mast is an open path infra-red gas analyser (Li-Cor, LI-7500, Fig. 10.2) to measures both CO2 and H2O. It uses the principle of radiation absorption by water and carbon dioxide molecules at certain wavelengths. A differential measurement is made to compare transmittance at a wavelength with strong absorption adjacent to a wavelength where absorption is negligible. For water vapour (carbon dioxide) the wavelength is 2.59 \(\mathrm{\mu m}\) (4.26 \(\mathrm{\mu m}\)) and the reference wavelength is 2.4 \(\mathrm{\mu m}\) (3.95 \(\mathrm{\mu m}\)). The ratio of light intensity at the two wavelengths is proportional to the amount of water vapour present.

The IRGA at URAO is an open-path rather than a closed-path instrument (where air is sucked down a tube into the instrument itself). The q specific humidity of water vapour is expressed in units of kg kg^-1. The absolute humidity (\(\text{kg m}^{-3}\)) is derived by taking the molecular weight of water into account (1 mol = 18 g = 0.018 kg) and similarly for carbon dioxide concentrations (molar mass 44 g \(\text{mol}^{-1}\)). The instruments are mounted close to each other at a height of 3 m. A Campbell CR3000 logger is used to record the data at a sampling rate of 10 Hz.

14.2.3. Wind and temperature profile mast (6.4 m)¶

A profile of 8 pulse cup anemometers and 4 platinum resistance thermometers (PRTs) are mounted at various heights (Table 14.5). The coincident temperature and wind profiles allow both stability and surface fluxes to be derived. Each anemometer produces electrical pulses at a rate proportional to its rotation speed. The PRT output voltage is proportional to the PRT resistance.

Table 14.5 measurement heights of temperature (T) and wind speed (U) at URAO¶
Variables measured	U&T	U	U&T	U	U&T	U	U&T	U
Height z (m)	0.56	0.80	1.12	1.60	2.24	3.20	4.48	6.40

14.2.4. Logging of sensors¶

Programmed data loggers sample the data at different time intervals. Raw samples (e.g. from EC system) or just statistics (e.g. an average from pyranometer) are recorded. During data processing calibration coefficients are applied.

14.3. Data from the Observatory¶

Data can be downloaded from: https://metdata.reading.ac.uk/ext/

Ask your instructor for download token in class if you need one.

14.3.1. Types of data¶

5 min averaged logger output.
- Includes individual radiation fluxes, soil heat flux, temperature (T), wind speed (WS), wind direction (Wdir), station pressure, rainfall, and relative humidity (RH).
Eddy covariances - 30-min averages.
- Fully processed EC fluxes: These have been subjected to the numerous corrections (Kotthaus and Grimmond 2012, 2014a) that are regularly undertaken for EC fluxes.
5-min WMO-standard processed output:
- This includes the wind profile data and the temperature profile data. Radiation data (make certain you use the corrected longwave radiation data)
0.1s Sonic Licor
- Raw EC data - these files are very large so do NOT download data until you know what you really want/need.

References: See References.