FAQ

1．General questions

• Q:1-01 What are the advantages of using this device?
  A:

  ①At the site, judgment can be made on where there is a groundwater path on the spot. In conventional survey, the place can be found only after measurement has been made and the survey data have been brought back and analyzed in many cases.

  ②The device is small and light in weight, and survey can be made by one person. Electrical exploration, or the like requires large equipment and multiple batteries and cables.
  The device makes the survey much easier.
  However, since conventional methods give higher accuracy, it would be better to use this device for rough survey to see where proper survey will be carried out.

  ③Very low cost
  For example, if electrical exploration is carried out, its cost is about 3 million yen at 1 km, with electrode intervals of 2.5 m and an exploration depth of 50 m.

• Q:1-02 Can the device be used by anyone?
  A:

  Anyone can use it after some practice and training on measurement.
  Any equipment that is generally used requires some practice. Such a level of practice and training on measurement is required to use the device. The practice and training on measurement are not especially difficult ones.
  This device is designed to give the same result to any users with internal calculation if it is properly used. However, since incorrect handling may give different results, measurement needs to be made by using the correct method of measurement. The following 3 points are important in order to obtain the correct result of measurement.

  1. Insert the sensor securely to the soil ground.
  2. Stand still while making measurement.
  3. Make measurement when there is little noise.

2．Questions about measurement

• Q:2-01 Roughly what is the maximum depth of measurement?
  A:

  Although it depends also on the quantity of water in the groundwater path, the depth of exploration is around 10 m.

• Q:2-02 Is it possible to measure the quantity of water flowing?
  A:

  At present, the quantity of water cannot be measured.

• Q:2-03 If there are multiple "groundwater paths," is it possible to identify the detailed positions of each such path?
  A:

  Although it may depend on the degree of such "detailed" positions, measurement can be made in units of meter without any problem.
  For example, when there are 5 groundwater paths at intervals of 20 cm, they may be separate groundwater paths when observed minutely, but an understanding that water appears to concentrate in the range of 1 m is more important at the site.

• Q:2-04 Can anyone read a "groundwater path" easily from observation data?
  A:

  Longitudinal and transversal measurement lines are drawn, and the intensity of sound is measured there at intervals of several meters.
  It should be understood that by means of this survey, a graph of sound distribution is made, and there is a groundwater path right below a peak of the sound.

• Q:2-05 When making measurement on a slope, how the points of measurement are determined? (Is there any way of determining the rule of thumb such that the points are roughly at a height above a relative height?)
  A:

  The places and intervals for making measurement vary with the purpose of survey. This is actually determined by the surveyor. If collapse is the purpose of survey in a mountainous area, the survey should be made roughly at intervals of 1 m, 2 m, 5 m or 10 m.
  It is an important point that intervals should be selected such that no groundwater path will be missed. Such intervals are determined by the widths of joints in geological structures.

• Q:2-06 Does the existence of a "groundwater path" mean that there is a sufficient quantity of water always flowing that can be detected?
  A:

  The quantity of water in a groundwater path changes at all times. As a result of such change, the intensity of sound varies on each day of survey.
  As for the good timing of measurement, the sound heard also becomes louder if measurement is made a couple of days after a rainfall.

• Q:2-07 Although the results of survey on wells by means of this device are shown, is the sound heard the same as the sound of a "groundwater path" on a slope?
  A:

  It is the same sound. The sizes of bubbles may vary with the grain sizes of soil particles, the sizes of gravel, etc. and the aeration sound given off may have different pitches, low and high, but the aeration sound itself has a universal property.

• Q:2-08 Is measurement affected by particular geological properties? Also, are there any judgment criteria as to whether measurement is possible or not?
  A:

  In the case of a mountainous area, there is hardly any place where no aeration sound is given off when a pickup sensor is inserted into the ground.
  Depending on geological properties, aeration sound is likely to be given off in some geological properties, and it is unlikely to be given off in others.
  It is considered that in gravel or sand-based geologies and geologies where cracks have developed, aeration sound is likely to be given off, for instance, in granite zones and in the geologies of accretionary wedges.
  Whereas, in clay-based geologies, for instance in zones of volcanic ash deposits, tuff, etc., aeration sound tends to be small.
  It may also be due to an influence of the ease with which groundwater permeates vertically (the source of sound is likely to be at a distance) in volcanic zones.

• Q:2-09 Can measurement be made in various types of soil ground such as those consisting of gravel, stone, earth, sand, etc.?
  A:

  Measurement can be made in any soil ground so long as a pickup sensor can be inserted into the ground.
  If the pickup sensor cannot be inserted into the ground such as an asphalt road, measurement can be made with a sensor disc (optional).
  However, the sensitivity decreases when measured with the sensor disc.
  A place that disables measurement is soil ground immersed with water such as a pool of water, and it is not a problem of the waterproofness of the pickup sensor, but because no sound is given off in soil ground immersed with water.

• Q:2-10 Can measurement be made around a river?
  A:

  Measurement is possible. However, measurement may become difficult depending on the place due to reasons such as loud river sound, heavy traffic, and the like.
  In the case of measurement to be made in a town, it requires some contrivances for making measurement in quiet conditions such as making measurement at night.

• Q:2-11 Is it possible to discern the difference between the sound heard form a groundwater path and noise (undesired sound) by listening to them?
  A:

  The difference can be discerned. The sound of water flowing underground is aeration sound such as burbling, bubbling, or pff, whereas other noises give off rustling sound or the like, of which tone is different from that of the aeration sound.
  However, it is important not to distinguish aeration sound among many noises, but to make measurement in a quiet environment.

3．Questions about the groundwater aeration sound measuring device

• Q:3-01 About how many hours can measurement be made with the battery of the device?
  A:

  Measurement can be made for 8 hours more with the battery.

• Q:3-02 What is the rough waterproof performance of the groundwater aeration sound measuring device?
  A:

  It has a simple drip-proof construction.
  The pickup sensor, headphone, connector areas of the serial cable, etc. are not waterproof.

• Q:3-03 Can the length of the sensor rod be extended? (Because measurement of the situation in an area deep underground may be desired depending on the place of measurement.)
  A:

  The sensor rod is not intended to be changed for the depth of measurement.
  It is intended to make the bottom of the pickup sensor contact and be fixed securely to the soil ground (ground surface).

  Type of sensor rod	Environment in which it is used
  Large (20 cm)	For soft soil ground where contact of the bottom of the sensor cannot be maintained
  Medium (15 cm)	Standard: For ordinary soil ground
  Small (10 cm)	For soil ground with a shallow soil layer (spraying works on a slope, etc.)
  Sensor disc	In a place where there is no soil such as bedrock or asphalt

• Q:3-04 What is the rough capacity of recording media for measurement data to be recorded in the device?
  A:

  The number of data that can be stored in the internal memory of the device is 800 cases.
  If the number of data becomes more than 800 cases, the data need to be collected by means of a PC.

• Q:3-05 What is the rough range of measurement frequencies of the device?
  A:

  With the pickup sensor, the peak frequency is 1.3 kHz; and the range of practical use is between 0.1 and 1.8 kHz.

• Q:3-06 At the time of power turn-on, is the sound loudness always set to "0"?
  A:

  It does not return to "0." The sound loudness set at the last operation is maintained.
  * In the settings at the time of delivery from the factory, the sound loudness is set to "0" prior to delivery.

• Q:3-07 Tell us about the method of import of recorded data and the method of processing the data.
  A:

  For the method of import and the method of processing, refer to explanations in these websites and the instruction manual attached to the product at the time of purchase.

• Q:3-08 What is the rough resolving power (resolution) of recorded data?
  A:

  The measurement recording unit performs sampling at a rate of 2 KHz by using an A/D converter with resolving power of 16 bit.
  For the calculation processing for the peak value (PD) and typical value, refer to the "Instruction Manual."
  Also, since the LINE OUT output is an output obtained by amplifying an analog signal, it has no resolving power.

4．Questions about the precautions for measurement, etc.

• Q:4-01 Is there anything that should be noted regarding the surrounding environment at the time of measurement?
  A:

  Survey should be carried out by selecting a date and time where there is little noise (sound) in the surrounding areas and at the right timing.
  When there is much noise, the noise is not eliminated by the filter only; it just reduces the noise.
  If measurement is made ordinarily in a quiet place such as mountainous area, there is no concern about noise.
  The noise that is most difficult to be removed with the filter is wind noise. It is recommended that survey be carried out on a day without wind or with little wind.
  However, even on a day with strong wind, the wind is not always so strong, and so it is possible to make measurement by choosing the time when there is little wind.
  Also, there may be the sound of a helicopter, airplane, or vehicle, but there will be no influence of such noise by waiting for the source of sound going far away.
  The point is that although there are various types of noise, measurement should be made by choosing the right time when there is no noise.

• Q:4-02 At the time of survey, is there any cause or object that gives hindrance around the area of measurement?
  A:

  The sources of sound (sources of noise) such as sound of an airplane, sound of a vehicle, voices of people talking, wind, etc. give hindrance to measurement.

• Q:4-03 Is it good time to make measurement after a rainfall?
  A:

  In the case of an ordinary rainfall, measurement can be made on the next day, but right after a heavy rainfall of a typhoon, etc., the level meter sways greatly in all the places, and a groundwater path may not be estimated correctly. For this reason, it is easier to estimate a groundwater path in the case of a heavy rain if measurement is made 2 - 3 days later.

• Q:4-04 It can be thought that at the time of a rainfall, the sound on the ground surface is also loud. Does such sound affect the measurement? (Also, is there any influence of any other weather conditions?)
  A:

  On a rainy day or a day with strong wind, correct survey is disabled by the great noise caused by the environment, and so such days are inappropriate to carry out survey.

• Q:4-05 Does the influence of wind cause any problem in mountain regions and areas around a dam or embankment, etc.?
  A:

  Wind has great noise and gives hindrance to measurement. Some contrivances are required such as covering the surrounding area of the sensor with a windshield.

• Q:4-06 If a metal, etc. is buried near the place of measurement, does it affect measurement?
  A:

  It may depend on the size and shape of the metal, but its size is around an ordinary gas pipe, it does not affect measurement (except in cases where the pipe becomes a source of sound such as giving off vibration, etc.).
  Also, it may become difficult to hear the sound if there is an iron plate above the groundwater vein.

• Q:4-07 It is thought that the propagation of sound varies with the soil property. Will a result with higher accuracy be obtained if prior survey of the soil property is carried out before measurement?
  A:

  By exploiting the survey and analysis of soil ground, the accuracy would become higher.
  However, because the soil ground survey requires cost and time, a simple method of survey in place for such survey is presented here.

5．Others

• Q:5-01 With regard to the business of a consultant, with what kinds of details the device can be utilized?
  A:

  Its possible use may include the survey of water flowing underground when the place of such water becomes a problem in a plan for design, construction work, etc.

• Q:5-02 Until now what kinds of methods have been used in the survey of groundwater paths?
  A:

  Survey is conducted by means of electrical exploration, airborne electromagnetic survey, 1 m depth earth temperature exploration, etc.
  Any of the methods has its advantages and disadvantages.

  ①Electrical exploration: Measurement takes time; a lot of work is required due to the great weight of the equipment, great efforts required for laying cables, etc.
  The equipment is expensive, costing 2 - 8 million yen.

  ②Airborne electromagnetic survey: Evaluation can be made in a wider area than with electrical exploration. Its resolving power is low.
  Since the survey is done by suspending a sensor from a helicopter, it is very expensive.
  Equipment + helicopter cost + 1 set of equipment = several million yen to dozens of million yen

  ③1 m earth temperature exploration: The earth temperature at a depth of 1 m is measured.
  Labor for making a 1 m hole is required. Measurement requires about 4 persons.
  The equipment cost is around 1 million yen.

• Q:5-03 I don't understand well what the sound of a groundwater path is like because I started to use the device a short while ago. Are there any judgment criteria or tips that are easy to understand about the sound of a groundwater path?
  A:

  The aeration sound that is given off by a groundwater path has the greatest intensity in the soil ground of sand and gravel, measurement should be made in a wet place of sand and gravel ground and in a place of sand and gravel ground that is not wet, and by comparing the sounds, you can understand the difference well.

• Q:5-04 Tell us about the weight of the device and a method by which the device is easy to be carried.
  A:

  The total weight of the pickup sensor, measurement recording unit, headphone, and battery is around 2.5 kg.
  Usually they are carried by putting them into a rucksack, etc.