Object's size estimation
based on photocounts distribution characteristics analysis

 

Essence

In case of object location which is at hundreds kilometers from laser location system, scattered field intensity in optical detectors area is low. Radiation influence on photodetector result is current impulses forming at the output, which can be considered to be separate equivalent occurrences – photocounts.

Photocounts registration in time period probability distribution law depends on dimensions of object surface part which has been irradiated. Scattered intensity field number of degrees of freedom  to a first approximation counted as quotient of coherent radiation area in detector aperture area  to this detector area  :

.

For most of real objects surface scattered radiation obey the Lambert law, therefore

,

where  – is  objects surface projection area on a perpendicular to vector of observations plane. Photocounts , depends on background radiation on photodetector effect. Photocounts  depends on objects surface scattered radiation on photodetector effect. If average counts  less then average of photocounts, then

.

To determine a kind of distribution  and scattered field radiation number of degrees of freedom estimation  on the basis of experimental observations, we must ascertain time interval start   in which we register scattered impulse. If object location conditions are known, one can find radiation scatter type of object, which overall dimensions are known to, by obtained value. One also can get diffusing disk (flat model ) radius  estimation, for which radiation scattered field statistic characteristics are equivalent to radiation field characteristics diffused by  by the same  value. We must provide experimental photocount samples representativeness to determine value correctly. Necessary number of location cycles determine from radiation propagation conditions and required errors of object dimensions estimation.

Experiments being carried out prove method efficiency. Radiation passed through rotating matted disk and replacement aperture with known diameter was detected by a photomultiplier tube. Fast AD converter and PC connected with it provided signal amplitude counts estimation, which are proportional to photocounts number, registered in observation time interval . After obtained signal amplitude counts estimations statistical treatment, registered photocounts distribution was counted and field radiation number of degrees of freedom was determined. Obtained number of degrees of freedom corresponds to object physical model dimensions.


Photocounts distribution obtained in experiments




 

Evaluation of photocurrent
on the photomultiplier tube output modeling


 

References

  • Себекин Ю.Н., Бурый Е.В., Загидуллин Р.Ш., "Оценка эффективности использования пачки импульсов в оптических локационных системах" // Алгоритмы обработки сигналов в радиоэлектронных устройствах: Сб. статей / Под ред. И.Б. Федорова. – М.: Изд.–во МГТУ, 1989.
  • E.V. Buryi, Yu.L. Smirnova, "Effect of the quantum nature of detecting low-intensity radiation on the distance measurement error in pulsed laser ranging", QUANTUM ELECTRON, 2004, 34 (12).