Underground survey apparatus

An underground investigation device that investigates an underground area while moving, the underground investigation device comprising:

• a transmission unit configured to transmit a pulse wave in a predetermined repetition cycle;
• a reception unit configured to receive a reflected signal of the pulse wave;
• a memory configured to store time waveform data of the reflected signal;
• storage means having a larger capacity than a capacity of the memory;
• a control unit configured to transfer the time waveform data from the memory to the storage means;
• and
• a signal processing unit configured to generate underground investigation data based on the time waveform data stored in the storage means, wherein
• the reception unit sets a measurement span for sampling the reflected signal by using, as a trigger, transmission of the pulse wave or reception of a reflected signal resulting from reflection of the pulse wave by a ground surface, samples the reflected signal in the measurement span, and stores time waveform data in the memory,
• the control unit transfers the time waveform data from the memory to the storage means after the measurement span, and
• the reception unit provides a trigger hold-off period in which the new measurement span is not set at least until transfer of the time waveform data is completed.