03-kirchner 10 khz - nasa · from < 60 khz to > 5 mhz (10 hz to 50 khz) 0 1000 2000 3000 4000...
TRANSCRIPT
PushingPushingPushingPushing Graz SLR Graz SLR Graz SLR Graz SLR fromfromfromfrom2 kHz to 10 kHz 2 kHz to 10 kHz 2 kHz to 10 kHz 2 kHz to 10 kHz repetitionrepetitionrepetitionrepetition raterateraterate
Georg Kirchner, Franz Koidl, Farhat Iqbal
Institute for Space Research
Austrian Academy of Sciences
Kötzting, May 2011
2IWF/ÖAW GRAZ
FromFromFromFrom 2 kHz to 10 kHz2 kHz to 10 kHz2 kHz to 10 kHz2 kHz to 10 kHz
Overview
� Basic problems & limitations of higher repetition rates
� #1: Overlap of transmit / receive pulses
� #2: Signal / Noise ratio for LEO & HEO satellites
� Question: What is the best (or highest ?) repetition rate ?
Kötzting, May 2011
� Technical problems, some solutions in Graz:
� Boosting the High-Q-Laser
� Adding the Riga ET for 10 kHz
� Keeping the Graz ET for 2 kHz (out of these 10 kHz)
� Routing of 2 kHz & 10 kHz start- and stop-pulses
� Setup and test results
3IWF/ÖAW GRAZ
At 2 kHz: Overlap occurs at every 75 km range difference
Noise Points / Second: LAGEOS 1 / night time
Overlap Avoidance OFF
0
100
200
300
400
500
600
700
20 30 40 50 60 70 80
Elevation [°]
Pts
/Sec
Basic problem #1: Overlaps
4IWF/ÖAW GRAZ
Graz / 400 µJ: During Overlaps > 50% noise
Ajisai (day 80) increased noise inside one overlap
(2634;160)
(2626;1060)
0
200
400
600
800
1000
1200
2600 2610 2620 2630 2640 2650 2660
One way Range[Km]
Noise
Poin
ts/sec
ond
During OVERLAP: Noise increases from 100 Hz to 1 kHz �
(Overlap Avoidance switched OFF)
5IWF/ÖAW GRAZ
If Overlap Avoidance is switched OFF…
Noise points/s vs. distance in [km] from detector into the atmosphere
0
250
500
750
1000
1250
0 5 10 15 20
Distance from detector[km]
Nois
e poin
ts/s
Day 79
Day 80
Day 81
Day 83
Day 96
Overlap backscatter: From distances up to 5 km; sometimes more …
6IWF/ÖAW GRAZ
The Overlap Problem
Kötzting, May 2011
� Overlap between transmit / receive pulses:
� Strong backscatter from first 5 km of atmosphere;
� Sometimes still backscatter from up to about 8 km of atmosphere
� Depends on elevation, actual atmospheric conditions etc.
� Should be avoided with Single Photon Systems (which are neededfor high rep rate systems with their low energy/shot)
� This limits the maximum repetition rate to about < 20 kHz
� Above that: Intrinsic / continuous backscatter
� Might become more tolerable with very low energy/shot
� Avoidable if transmit / receive telescope are separated (some 10 m)
7IWF/ÖAW GRAZ
Kötzting, May 2011
Basic problem #2: Signal / Noise Ratio
Graz Laser: Constant ENERGY Laser (0.4 mJ)
Wanted: Constant POWER Laser: Not (yet) available (?)
Constant Power Laser:
Energy per Pulse decreases with Rep Rate
0.01
0.1
1
10
100
1000
10 100 1000 10000 100000
Repetition Rate [Hz]
Energ
y / P
uls
e [m
J]
1 W Laser
5 W Laser
0.8 W Graz Laser
Graz Laser
‘Useful kHz‘ SLR Range’10 Hz‘ Systems
8IWF/ÖAW GRAZ
Kötzting, May/2011
Another limitation: Signal / Noise Ratio
- Increasing the laser rep rate: Energy per shot decreases: =>Decreases signal ����
- Increasing the laser rep rate: Noise increases: =>Increases noise ����
- Each Range Gate can produce a noise point (20-50% in Graz daylight)
- SPAD dark noise increases: from 60 kHz@10 Hz to >5000 kHz@50 kHz
- Decreasing signal ���� => S/N Ratio => S/N Ratio => S/N Ratio => S/N Ratio ↓↓↓↓↓↓↓↓
Increasing noise ����
- Return identification gets difficult at low S/N ratios
C-SPAD dark noise: Increases with Rep Rate:
From < 60 kHz to > 5 MHz (10 Hz to 50 kHz)
0
1000
2000
3000
4000
5000
6000
0 10000 20000 30000 40000 50000
Repetition Rate [Hz]
C-S
PA
D D
ark
No
ise
[kH
z]
Dark Noise
C-SPAD: Dark Noise
increases with repetition rate:
e.g. 3 MHz noise at 20 kHz
9IWF/ÖAW GRAZ
Assumed: 5 W Constant Power Laser / C-SPAD / Graz Atmosphere:
LEO: Significant increase of returns / s at least until 10 kHz
Kötzting, May/2011
LEO: How many returns per second can we expect ???
LEO: Returns per Second vs. Reptition Rate
5 W Constant Power Laser, Average Graz Weather
10
100
1000
10000
100000
10 100 1000 10000 100000
Repetition rate[Hz]
Ret
urn
s /
s
Champ 30°
Champ 70°
Envisat 30°Envisat 70°
Ajisai 30°
Ajisai 70°
2 kHz 10 kHz
10IWF/ÖAW GRAZ
Assumed: 5 W Constant Power Laser / C-SPAD / Graz Atmosphere:
HEO: NO increase of Returns / s above a few 100 Hz;
LAGEOS: NO increase of Returns / s above a few kHz
HEO: How many returns per second can we get ???
HEO: Returns per Second vs. Reptition Rate
5 W Constant Power Laser, Average Graz Weather
1
10
100
1000
10 100 1000 10000 100000
Repetition rate[Hz]
Ret
urn
s /
s
Lageos at 30°Lageos at 70°Etalon at 30°Etalon at 70°GPS at 30°GPS at 70°
2 kHz 10 kHz
11IWF/ÖAW GRAZ
FromFromFromFrom 2 kHz to 10 kHz2 kHz to 10 kHz2 kHz to 10 kHz2 kHz to 10 kHz
Preliminary Conclusions for higher repetition rates:
� 10 kHz Laser Repetition Rate is a good compromise
� Overlaps still can be avoided
� Direct increase of returns per second for LEO
� Still some increase for LAGEOS
� Limited additional value for HEO satellites (but 2 kHz still okay here)
Kötzting, May 2011
� Can be achieved in Graz with minor changes, no big investments ☺
� Boosting the High-Q-Laser: Needs only a new Pockels Cell Driver
� Needs Riga ET for 10 kHz: Already available
� Needs an additional Windows PC
� Needs a new PDM (Pulse Distribution Module)
12IWF/ÖAW GRAZ
Graz 2 kHz Laser: Limits for higher Rep Rates
Oscillator + Regenerative Amp: CW Pumped => Could deliver up to ≈ 50 kHz !!!
But: Original Pockels Cell: 5 kHz max; replaced by new Pockels Cell: 10 kHz max.
Post Amp: Pulsed Pumping: 2 kHz max. limited; no way to increase it ….
SEED (SESAM):
70 MHz
Isolator
Regenerative
Amp.
Lambda/2
P.C.
HR
Lambda/4
Post Amp.
Start Det.SHG
CW
URDM
URDM
CW
URDM
Pulsed
13IWF/ÖAW GRAZ
Post Amp: Remains at 2 kHz; Osc.+ Regen: 10 kHz
Osc. + Regen. Amp.: CW Pumped => generating pulses at 10 kHz
Post Amp: Pulsed Pumping: Remains at 2 kHz max
New Pockels Cell installed: Allows up to 10 kHz (Regen. Amp.)
Therefore: Pulses with alternating energy:
1 pulse amplified by post amp: 400 µJ
Next 4 pulses NOT amplified by post amp: 80 µJ
2 kHz: 400 µJ (each pulse)
10 kHz: 1*400 µJ, 4*80 µJ …
80 µJ
400 µJ
Standard HQ Laser: 2 kHz
400 µJ / Pulse; 0.8 W
400 µJ
Upgraded HQ Laser: „10“ kHz
400 µJ / 80 µJ Pulse; 1.44 W
14IWF/ÖAW GRAZ
Graz ET:
2 kHz
HQ Laser C-SPADPulse Distribution
Module PDM
StopsStarts
Starts +
Sto
ps
DOS PC ISA FPGA Win PC
Riga ET:
10 kHz
max
Graz: 10 kHz Setup …
Sta
rts
+ S
tops
Start/Stop pulse colors: Symbolic to indicate STRONG (green) and WEAK (red) pulse energy …
15IWF/ÖAW GRAZ
First test results with Graz 10 kHz SLR
Return Rate Increase vs. Perigee:
10 kHz / 2 kHz
1.0
1.5
2.0
2.5
3.0
100 1000 10000 100000
Satellite Perigee [km]
Retu
rn R
ate
In
cre
ase F
acto
r
Laret
Jason-2
Lageos-2
Etalon-21.44 W / 0.8 W = 1.82
Max. Increase: 10 kHz / 2 kHz = Factor ≤ 5.00
Min. Increase: 1.44 W / 0.8 W = Factor of 1.82
Envisat
1.44 W @ 10 kHz / 0.8 W @ 2 kHz = 1.82; for Single Photons, we will arrive at this ratio;
For Single Photon Satellites (HEOs and LAGEOS): Theoretical Factor 1.82 expected;
For Multi –Photon Satellites (LEOs): The Factor will increase, according to received energy ( distance …)
16IWF/ÖAW GRAZ
What we expect from High-Q-Laser et al:
CONSTANT POWER LASER; e.g. 5 W:
100 Hz / 50.0 mJ for HEO satellites
10 kHz / 0.5 mJ for LEO satellites
- Graz 10 kHz system is still under test – no 10 kHz NPs yet distributed
- DOS programs still ‚see‘ a 2 kHz system – Win PC handles RIGA / „10“ kHz
First test results with Graz 10 kHz SLR
17IWF/ÖAW GRAZ
New Dome in Graz New Dome in Graz New Dome in Graz New Dome in Graz ---- butbutbutbut still still still still „„„„oldoldoldold““““ 2 kHz2 kHz2 kHz2 kHz…………
Thank you ☺☺☺☺