LOCATION
LOCATION
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When monitoring over time the behaviour of meteorological parameters that characterise the underground climate, first of all air temperature, it is necessary to carefully evaluate instrument placement.
When monitoring over time the behaviour of meteorological parameters that characterise the underground climate, first of all air temperature, it is necessary to carefully evaluate instrument placement.
It is often assumed that cave temperature is uniform and stable over time; this is not the case. Air temperature in caves is in fact subject to daily, seasonal and multi-year variations whose magnitude depends on distance from entrances and on air circulation.
It is often assumed that cave temperature is uniform and stable over time; this is not the case. Air temperature in caves is in fact subject to daily, seasonal and multi-year variations whose magnitude depends on distance from entrances and on air circulation.
Air temperature sensor and ultrasonic anemometer
INSTRUMENT INSTALLATION
INSTRUMENT INSTALLATION
Drilling an inclined hole for rock temperature sensor installation
The sensor for air measurement must be placed at least 50 cm away from rock walls, even simply hung from the ceiling or along a cord stretched between walls.
The sensor for air measurement must be placed at least 50 cm away from rock walls, even simply hung from the ceiling or along a cord stretched between walls.
Nearby, a hole can be drilled in the rock with a bit of sufficient diameter to insert a temperature probe. The monitored rock zone must be relatively dry, have a regular surface and be compact, that is, free from fractures or small conduits. The hole must have a depth of approximately 40 cm and be slightly inclined upwards, so that water does not collect in it. The space between cable and rock must be filled towards the outside of the hole with sealing material.
Nearby, a hole can be drilled in the rock with a bit of sufficient diameter to insert a temperature probe. The monitored rock zone must be relatively dry, have a regular surface and be compact, that is, free from fractures or small conduits. The hole must have a depth of approximately 40 cm and be slightly inclined upwards, so that water does not collect in it. The space between cable and rock must be filled towards the outside of the hole with sealing material.
The ideal location is usually in environments that have a few metres of width, both laterally and in height, free from direct air currents and distant from significant water flows such as underground streams or strong inflows from shafts. It may instead be of interest to monitor small water seepages, whose temperature is linked to that of the rock in the overlying percolation zone.
The ideal location is usually in environments that have a few metres of width, both laterally and in height, free from direct air currents and distant from significant water flows such as underground streams or strong inflows from shafts. It may instead be of interest to monitor small water seepages, whose temperature is linked to that of the rock in the overlying percolation zone.
For this reason, to have a complete picture of the thermal conditions present in a cave, it is important to monitor, together with air and water, also rock temperature. Since most commonly used dataloggers are equipped with two probes, using two units allows the fourth sensor to be used for an additional measurement of air or rock temperature.
For this reason, to have a complete picture of the thermal conditions present in a cave, it is important to monitor, together with air and water, also rock temperature. Since most commonly used dataloggers are equipped with two probes, using two units allows the fourth sensor to be used for an additional measurement of air or rock temperature.
Air temperature sensor location far from rock face
Container with water temperature probe of a secondary outlet
For water temperature measurement, the probe must be kept immersed in a small container, little larger than necessary to accommodate the sensor, into which drip water or water from a small seepage is conveyed with a funnel or a small sheet. It is evident that any water collection system alters its temperature, especially when the flow rate is low, so we must reduce its dimensions to a minimum. If we wish to measure wall flow, it may be convenient to drill a hole in the rock a few centimetres deep, this time inclined downwards, and insert the temperature probe directly into it.
For water temperature measurement, the probe must be kept immersed in a small container, little larger than necessary to accommodate the sensor, into which drip water or water from a small seepage is conveyed with a funnel or a small sheet. It is evident that any water collection system alters its temperature, especially when the flow rate is low, so we must reduce its dimensions to a minimum. If we wish to measure wall flow, it may be convenient to drill a hole in the rock a few centimetres deep, this time inclined downwards, and insert the temperature probe directly into it.
Sensor placement
Dataloggers can be hung on walls with cord or fixed to them with anchors. In the case of dataloggers also equipped with an internal sensor, it is preferable to hang them or insert insulating material between the datalogger and the rock.
Dataloggers can be hung on walls with cord or fixed to them with anchors. In the case of dataloggers also equipped with an internal sensor, it is preferable to hang them or insert insulating material between the datalogger and the rock.
Generally, particular protections are not necessary, given that it has been said that the station must be located in areas free from conspicuous water inflows or subject to flooding.
Generally, particular protections are not necessary, given that it has been said that the station must be located in areas free from conspicuous water inflows or subject to flooding.
In any case, it is advisable to choose locations that are easily accessible in order to make data download operations straightforward and rapid which depending on the dataloggers used require connection with a computer via a connection cable or bluetooth connection via a tablet or smartphone.
In any case, it is advisable to choose locations that are easily accessible in order to make data download operations straightforward and rapid which depending on the dataloggers used require connection with a computer via a connection cable or bluetooth connection via a tablet or smartphone.
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