Digital signal processing in optical systems used for ranging applications

• US 7,895,007 B2
• Filed: 10/23/2009
• Issued: 02/22/2011
• Est. Priority Date: 11/07/2007
• Status: Active Grant

• Current Assignee: LeddarTech, Inc.
• Original Assignee: Institut national d'optique
• Inventors: Cantin, Daniel, Levesque, Marc, Babin, François
• Primary Examiner(s): Le; John H
• Application Number:
  US12/604,824
• Publication Number:
  US 20100039637A1
• Time in Patent Office: 487 Days
• Field of Search: 702 66- 76, 702/158, 702/176, 250/559.38, 356/5.03, 356/5.08, 367/99, 342/109, 342/175
• US Class Current: 702/69
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 7/484 Transmitters
• CPC Class Codes: G01S 7/4868 Controlling received signal intensity or exposure of sensor
• CPC Class Codes: G01S 7/487 Extracting wanted echo signals , e.g. pulse detection

Abstract

Methods and apparatuses for reducing the response time along with increasing the probability of ranging of optical rangefinders that digitize the signal waveforms obtained from the pulse echoes returned from various types of objects to be ranged, the pulse echoes being too weak to allow successful ranging from a single waveform or the objects being possibly in motion during the capture of the pulse echoes. In a first embodiment of the invention, the response time at close range of a digital optical rangefinder is reduced by using a signal averaging process wherein the number of data to be averaged varies with the distance according to a predetermined function. In a second embodiment of the invention, the probability of ranging objects in motion along the line of sight of a digital optical rangefinder is increased and the object velocity measured by performing a range shift of each acquired signal waveform prior to averaging. In a third embodiment of the invention, the signal waveforms acquired in the line of sight of a digital optical rangefinder are scanned over a predetermined zone and range shifted and averaged to allow for early detection and ranging of objects that enter in the zone.

Claims

1. An apparatus for optically sensing a remote object, said apparatus comprising:

an optical emitter module for sending optical pulses towards said object;

an optical receiver module for receiving optical signals reflected by said object and for converting said optical signals into digital signal waveforms; and

a control and processing unit for processing said digital signal waveforms, said control and processing unit being adapted to;

(a) sample said digital signal waveforms at a predetermined number N_p of range values R_i, i=1, 2, 3, . . . , N_p;

(b) select a function N(R_i) that gives the number of data samples to be averaged for each range value R_i;

(c) compute the average of a quantity N(R_i) of signal data sampled at a first range value R_i each time a quantity N(R_i) of signal waveforms has been generated;

(d) update an average signal amplitude previously measured at said range R_i with the result computed above; and

repeating step (c) for each range value R_i,

whereby the response time of said apparatus is minimized for each range R_i by averaging only the quantity N(R_i) of data sampled at each range R_i that is required to get a desired signal to noise ratio at each range R_i.

2. An apparatus according to claim 1, comprising a laser rangefinder.

3. An apparatus according to claim 1, comprising a lidar.

4. An apparatus according to claim 1, said optical emitter module comprising at least one light-emitting diode.

5. An apparatus according to claim 1, wherein said function N(R_i) increases monotonically with said range value R_i.

6. An apparatus according to claim 1 wherein said function N(R_i) is given by a polynomial expression of order comprised in the interval of 1 to 4.

7. An apparatus according to claim 1, wherein said function N(R_i) is given by the square of the ratio between a desired value for the signal to noise ratio of the processed signal waveforms and the real signal to noise ratio measured at each range value R_i for a single raw signal waveform.

8. A method for optically sensing a remote object using an optical sensing apparatus, comprising the steps of:

(a) sending optical pulses towards said object,

(b) receiving the optical signals reflected by said object,

(c) converting said optical signals into digital signal waveforms, each of the said digital signal waveforms being formed of data sampled at a predetermined number N_p of range values R_i, i=1, 2, 3,. . . , N_p, and

(d) numerically processing said digital signal waveforms, said numerically processing step comprising;

(d1) selecting a function N(R_i) that gives the number of data samples to be averaged for each said range value R_i,

(d2) computing the average of a quantity N(R_i) of signal data sampled at a first range value R_i each time a quantity N(R_i) of signal waveforms has been generated,

(d3) updating an average signal amplitude previously measured at said range R_i with the result computed in step (d2),

(d4) repeating steps (d2) and (d3) for each said range value R_i,

wherein the response time of said apparatus is minimized for each said range R_i by averaging only the quantity N(R_i) of data sampled at each said range R_i that is required to get a desired signal to noise ratio at each said range R_i.

9. A method according to claim 8 wherein said optical sensing apparatus comprises a laser rangefinder.

10. A method according to claim 8 wherein said optical sensing apparatus comprises a lidar.

11. A method according to claim 8 wherein said optical sensing apparatus uses at least one light-emitting diode for sending optical pulses towards said object.

12. A method according to claim 8 wherein said function N(R_i) increases monotonically with said range value R_i.

13. A method according to claim 8 wherein said function N(R_i) is given by a polynomial expression of order comprised in the interval of 1 to 4.

14. A method according to claim 8 wherein said function N(R_i) is given by the square of the ratio between a desired value for the signal to noise ratio of the processed signal waveforms and the real signal to noise ratio measured at each range value R_i for a single raw signal waveform.