PURPOSE: To improve the measuring precision by correcting a compaction state of a ground surface measured by an alpha-ray densitometer and aneutron moisture gage by way of measuring a clearance between a measuring instrument and the ground surface. ;CONSTITUTION: A radioactive rays are irradiated on a ground surface by mounting alpha-rays source 1 and a neutron source 2 on an iron plate made sled 9, and the sled 9 is moved on a ground by a tractor. Thereafter, a clearance between a meansuring instrument and the ground is measured by measuring a fast neutron scattered on the ground surface by an He-3 counter 5 mounted on the sled 9. Subsequently, moisture of the ground surface is measured by instrumenting a thermal neutron scattered on the ground surface by an He-3 counter 6. Furthermore, density of the ground surface is measured by measuring alpha-rays scattered on the ground surface by a GM counter 7. Thereafter, a data processor part 8 previously memorizing a data for correction collects, selects, computes and corrects each computing rate data instrumented by each detection part and displays a compaction result. Consequently, it is possible to precisely carry out instrumentation at real time and to adopt a countermeasure of re-rerolling compaction, etc., in a short period of time.;COPYRIGHT: (C)1996,JPO
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