Download - 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