3D Ladar

SEMINAR PRESENTATION

05 /08/2010

PRESENTED BYMANOJ KUMAR.M,S7-EC,ROLL.NO.15,LMCST.

CONTENTS1. INTRODUCTION.2. BASIC PRINCIPLE OF OPERATION.3. MICROCHIP LASER TRANSMITTER.4. OPTICAL TO ELECTRICAL CONVERSION.5. PIXEL TIMING CIRCUITS.6. IMPLIMENTATION SCHEMATICS.7. CAPTURED IMAGES.8. PIXEL SCALING.9. GEO MAPPING.10. PLOTTING OF SCANNED ECHOES.11. ADVANTAGES.12. APPLICATIONS.13. CONCLUSIONS.14. REFERENCE.

1.INTRODUCTIONRadar means radio detection and ranging.

An initial RADAR system transmits electromagnetic pulses into remote target in space, and then the echo is detected and measures the range.

The pulse radar is scanned by steering antennas measure the direction.

By the modification of initial radar by laser transmitter and receiver is LADAR.

Developed by Lincoln Lab for Defense Advanced Research Project (DARPA) agency in USA is equivalent to DRDO in India.

2.BASIC PRINCIPLE OF OPERATION

The laser technology for the ladar is based on diode-pumped solid state microchip lasers that are passively Q-switched.

The detector technology is based on arrays of avalanche photodiodes (APDs) operating in Geiger mode,

An auxiliary detector marks the time at which the laser pulse is emitted. The reflected light is imaged onto a two-dimensional array of detectors.

The detectors measure the time of flight of the reflected light. The time of flight is proportional to the distance between the point of reflection distance on the target and the sensor system. With range measured for each pixel, the ladar produces a 3D (angle-angle range) image.

3.MICROCHIP LASER TRANSMITTER

Passively Q-switched microchip lasers are constructed by diffusion-bonding laser-gain medium[Nd:YAG, ] to a short piece of saturable absorber[YAG (Cr4+:YAG)]

The pump-side face of the structure is coated to transmit the pump light and reflect the laser light. The output face is coated tube partially reflecting at the lasing frequency, provides both feedback and laser output

The intracavity saturable absorber prevents the onset of lasing until the average inversion density within the cavity reaches a critical threshold.

At that point, the onset of lasing produces a high intracavity optical field that saturates the absorber, resulting in a Q-switched output pulse a few hundred picoseconds long.

For high pulse energies, the input and output faces of the composite structure are capped with short pieces of undoped YAG in order to increase the damage threshold

The Sources of laser used in Ladar are Nd:YAG in military application (R=2000m to10k.m.) Chemical lasers (CO2 LASERS penetrates through atmosphere fog & smoke) [Hidrogen fluride & Duterium fluride Lasers have higher efficiencies and they have high output energies) Solid state laser (They cannot provide a the necessary spectral purity to utilize phase processing of LADAR signals)

.

4.OPTICAL TO ELECTRICAL CONVERSION

Geiger-Mode Avalanche Photodiode:Photon-to-Digital Conversion

Digitally encodedphoton arrival time

photon

APD

Single pixel

Digitaltimingcircuit

Lensletarray

APD array

Focal plane

CMOS array

Geiger-mode operation biases diode above breakdown, generating charge avalanche upon generation of a single photoelectron

• Yields single-photon- counting sensitivity

• Current generated is enough to trigger CMOS timing logic

• Result is digital time of photon arrival with no amplifier noise

It consists of a two-dimensional array of APDs bonded to a commensurate array of timing electronics.

The APDs are biased to operate in Geiger mode, in which an electron-hole pair generated by a single photon initiates an avalanche process that results in a large current pulse.

The high-amplitude current pulse triggers high-precision timing circuitry.

A TTL pulse generated by the Geiger-mode detection of a single photon

5.SINGLE PIXEL TIMING CIRCUITS

A common clock broadcast to all the pixels controls timing. The clock runs a feedback shift register that counts through a predetermined sequence.

When the APD fires, the resulting signal triggers a latch, which stops the timing register. The data are then read out from each of the pixels in serial fashion

The clock is delayed in phase by 90 ° to provide higher temporal resolution.

Bridge bonding:The CMOS chip is epoxies to the APD wafer, and then sloped vias are etched through the epoxy and metallized to make an electrical connection between the APD and the timing circuit. Before etching thinning is done. Thinning enables the bridge-bonding process and is necessary to achieve a high detection probability

32x32 ArraySilicon (Visible), InGaAs (1-m)

32 x 128 ArrayGeiger-Mode APD Arrays Bonded to CMOS Timing Circuitry

Technology advantages: Extreme sensitivity (single photon) Fine range resolution (< 10 cm) Fully integrated - digital output of range image Scalable to large array sizes

Measuring the time between transmission and return of a signal

Measuring the intensity of the returned signal

Using stereo vision

Using Laser striping

Using optical flow

6.FIRST IMPLEMENTATION SCHEMATICS

It a transportable 3Dladar system. This first-generation system, called a brassboard

The Geiger-mode APD detector array is a 4X4 prototype. The timing electronics are external

7.CAPTURED 3D IMAGES FOR 128×128 ARRAY

Image of a Chevrolet Astro van obtained from the 3D-ladar brassboard.

10.PLOTTING OF SCANNED ECHOES FROM THE GROUND

12.APPLICATIONS.Geo mapping of the earth and location

detection.Detection of hills, sea, valleys for traffic

route determinations.To monitor the environment to provide

air pollution location Pixel ScalingAutomatic air traffic landing systemsDetection of huge ice bergs on the sea .

GEO MAPPING

PIXEL SCALING

COMPARISON WITH RADAR

1.LASER is used2.Shorter wavelength3.Beam width is less4.High resolution5.Photo detectors are

used for light reception6.Atmospheric effects are

severe

1.Radio wave is used2.Higher wavelength3.Beam width is high4.Resolution is less5.Field current

conversion is used in RF reception

6.Atmospheric effects are less severe

LADAR RADAR

ADVANTAGESLow power high efficient CMOS based system design.3D reconstruction is easily possible.Ground based control and location is possible.Precisely capture the location. Effect of noise echo is completely eliminated by

windowing detection.Provides higher resolution

Depends on weather

Depends on reflection of the surface

Particles in air will affect the range

CONCLUSIONSLadar is, in the correct environment, better suited for

speed detectionModern laser radar system combine the capabilities

of radar and optical system to allow simultaneous measurement of range. Reflectivity ,velocity,temperature and elevation angle

DSP technique capable of handling the extremely high information rate available from LADAR operating bandwidth

By using both ladar & radar we can achieve maximum detection capabilities

14.REFERENCEBlair, J.B., Coyle, D.B., Bufton, J.L., Harding, D.J., 1994.

Optimisation of an airborne laser altimeter for remote sensing of vegetation and tree canopies. Proc. Int. Geosci. Remote Sens. Symp. II, 938–941.

Bufton, J.L., Blair, J.B., 1996. Space laser altimetry: laser engineering for multi-beam applications. Rev. Laser Eng. 24, 1285–1292.

Bufton, J.L., Garvin, J.B., Cavanaugh, J.F., Ramos-Izquierdo, L., Clem, T.D., Krabill, W.B., 1991. Airborne lidar for profiling of surface topography. Opt. Eng. 30, 72–78.

Dubayah, R., Blair, J.B., Bufton, J.L., Clark, D.B., Ja´Ja´, J., Knox, R., Luthcke, S.B., Prince, S., Weishampel, J., 1997.

GUIDED BY

DEPT: OF ELECTRONICS AND COMMUNICATION

LOURDES MATHA COLLEGE OF SCIENCE & TECHNOLOGY

KUTTICHAL