| 摘要 |
Methods and apparatus are described for generating and transmitting signals in accordance with a sequence which defines the time relationship of the signals. Each signal has a band width covering several octaves and may be a pulse. During a transmission interval the repetition frequencies of the signals monotonically sweep in a coherent relationship over bands restricted to an octave such that the spectrum of the sequence has substantially constant energy over a frequency range much larger than an octave. The autocorrelation function of the sequence is characterized by an absence of side lobes which would indicate false targets or produce a high noise level upon processing of the signals in an echolocation system, such as a geophysical exploration system in which the seismograms are constructed by cross correlation of the signals which are received from the geological reflection surfaces with a stored replica of the transmitted signals. The signals can be generated by a plurality of sources all of which operate during the transmission interval, thus enabling the transmission of increased energy into the medium (viz., the seismic signal power injected into the earth). |
