Method: A very short-pulse electromagnetic signal is coupled into the earth by means of a specially designed antenna. The reflected signals are detected by a second antenna and time delays of the various radar reflections from sub-surface targets are measured on an RF oscilloscope. Oscilloscope Polaroid photography of radar A-scope output. Frequencies used are typically between 20 and 150 MHz depending on the application. New high power design achieves a transmitted power of 30 kilowatts. Not destructive or harmful to the environment in any way. The equipment is small and light weight and easy to use underground. Very useful in confined spaces, or in vertical mountings for viewing through a wall or hillside, or in other situations where a cart radar can not be used. Radar can be monostatically or bistatically mounted. Very good distance resolving power. Does not generate RFI or electrical interference. Battery powered if AC power not convenient.
Method: A very short-pulse electromagnetic signal is coupled into the earth by means of a specially designed antenna. The reflected signals are detected by a second antenna equipped with a high-gain built in preamplifier. The antennas and associated electronics are mounted on a wheeled-cart for ease in traversing large areas of the surface. (Ski mounting of radar is available for use on sand or ice and snow surfaces). Frequency used is typically 150 MHz. Radar output processed by a personal computer and a false-color display is used. Output is recorded on video tape or hard disk with voice comments and cart-position information. Color print outs of the data are available. Very good distance resolving power. Does not generate RFI or electrical interference. Battery operated when AC power is inconvenient.
Method: A very short-pulse electromagnetic signal is coupled into the earth by means of a specially designed antenna axially mounted in a four-inch diameter cylinder. The reflected signals are detected by a second cylindrical borehole antenna equipped with a high-gain built in preamplifier. The antennas can be lowered up by means of RF cable reels to 400 feet deep in borehole. Radar output is displayed on oscilloscope screen for A-scope photographing. Antennas can be used in monostatic or bistatic configuration. Very good distance resolving power. Does not generate RFI or electrical interference. Battery operated when AC power is inconvenient. Transmitter generates 30 kilowatts peak power which is a factor of 30 times higher than any known GPR now on the market. The frequency used is 150 MHz.
In the past there has been no easy way to measure the thickness of concrete slabs or footings. Has the contractor poured to meet specs or is the slab only attaining the correct thickness at one or two points? Are the footings under my building as deep as they should be? Why has my slab cracked?
Similar question often arise regarding concrete foundational piers. Are the concrete piers under my house as deep as shown on the blueprints? Were they poured all at once or on subsequent days? Have piers cracked or been broken since they were installed?
What is the depth of soil over bedrock and how competent is the bedrock?
A unique, one-of-a-kind High Frequency Seismic Sounder can often provide answers about concrete thickness and depth not obtainable any other way except by direct excavation.
High Frequency Seismic Sounding is a new geophysical method which can be very helpful when probing into concrete or solid rock. (The method is not suitable for direct probing into soil since compressional seismic waves are difficult to generate into soils). Two seismic transducers are employed. A transmitted pulse is introduced into the concrete through one of these transducers and the second unit is used as a receiver. A thin film of water-soluble gel is used at the transducer-concrete interface to achieve the necessary coupling for sound waves in and out of the medium. A short pulse up to several hundred watts in intensity is used. The frequency chosen is normally between 1000 and 30,000 Hz (1-30 kHz).
Since the velocity of propagation of sound waves in concrete is accurately known, the time delay of reflected signals is measured from an oscilloscope display. The results yield the thickness of concrete slabs, foundation depths or pier depths. Cracks and fractures in concrete piers frequently show up on the HF Seismic Sounder. In some situations the sounder can measure depths of fill over bedrock under a concrete slab. Voids and cavities under a slab are usually detectable.
In order to successful sound into concrete the seismic transducers need to be emplaced directly over the area to be examined. In the case of piers or footings one can usually probe through wooden headers and beams provided they are in good mechanical contact with the concrete beneath. The sounder can also be used for viewing horizontally into concrete. In this case the transducers are pressed tightly against the concrete and clamped in place to assure intimate contact.
Most surveys using the High Frequency Seismic Sounder can be completed in one working day with results available immediately at the site.
Top: CW: Cart Radars in use on ice and on city street, Portable radar in use in wet underground tunnels. Bottom: CW: Superstition Mountains, Philippines, Philippines, Borehole radar at Victorio Peak, WSMR, New Mexico.
I am now retired from Geophysical Work. Contact International Radar Consulnatnts, Inc. for expert geophysical help.