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URAO.rst
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URAO.rst
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.. _URAO:
URAO
====================
.. #TODO: Links to other relevant materials
.. _safety:
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 <https://www.bb.reading.ac.uk/webapps/portal/execute/tabs/tabAction?tabId=_110_1&tab_tab_group_id=_154_1>`_).
.. 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.
Instruments
-----------
Overview
~~~~~~~~~~~~~~~~~~~~~~~~~
- Wind
.. _urao_wind:
.. csv-table:: Wind-related measurements at URAO
:file: URAO-wind.csv
:widths: auto
:class: longtable
:header-rows: 1
:stub-columns: 1
- Heat and humidity
.. _urao_temp:
.. csv-table:: Temperature&humidity-related measurements at URAO
:file: URAO-temperature.csv
:widths: auto
:class: longtable
:header-rows: 1
:stub-columns: 1
- Radiation
.. _urao_rad:
.. csv-table:: Radiation-related measurements at URAO
:file: URAO-radiation.csv
:widths: auto
:class: longtable
:header-rows: 1
:stub-columns: 1
- Other
.. _urao_other:
.. csv-table:: Other measurements at RUAO
:file: URAO-other.csv
:widths: auto
:class: longtable
:header-rows: 1
:stub-columns: 1
Eddy Covariance (EC) mast
~~~~~~~~~~~~~~~~~~~~~~~~~
The EC mast at the URAO has a **sonic anemometer** (Gill R3, :numref:`gill`) 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, :numref:`li7500`) 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.
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 (:numref:`urao_heights`).
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.
.. _urao_heights:
.. csv-table:: measurement heights of temperature (T) and wind speed (U) at URAO
:file: URAO-heights.csv
:widths: auto
:header-rows: 1
:stub-columns: 1
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.
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.
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 :ref:`refs`.