The application of the streak camera with the circular sweep for the satellite laser ranging is described. The Modular Streak Camera system employing the circular sweep option was integrated into the conventional Satellite Laser System. The experimental satellite tracking and ranging has been performed. The first satellite laser echo streak camera records are presented

Hamal, Karel

Kirchner, Georg

Koidl, F.

Prochazka, Ivan

English

NASA Technical Reports Server

N94-15574
THE FIRST SATELLITE LASER ECHOES
RECORDED ON THE STREAK CAMERA
K.Hamal, I.Proch_ka
Faculty of Nuclear Science and Physical Engineering, Czech Technical University
Brehova 7,115 19 Prague 1,Czechoslovakia,
Phone/fax +42 2 848840, telex 121254 fjfi c, E-mail TJEAN@CSEARN.BITNET
G.Kirchner, F.Koidl
Austrian Academy of Sciences,Lustbuenel Observatory
A-8042 Graz, Austria, Phone +43 316 472231
ABSTRACT
The application of the streak camera with the circular sweep for the satellite laser ranging
is described. The Modular Streak Camera system employing the circular sweep option was
integrated into the conventional Satellite Laser System. The experimental satellite tracking and
ranging has been performed. The first satellite laser echo streak camera records are present-
ed.
GENERAL
The laser ranging of the artificial Earth satellites, the Moon and the long ground baselines
is an attractive and rapidly developing technique. The laser ranging precision and accuracy
is gradually increasing, it reaches one centimeter level at present. The goal for nineties,
requested by the data users, is the satellite laser ranging to artificial satellites with millimeter
accuracy. The existing pulsed laser ranging systems are using short pulse lasers of 20-200
picoseconds at 532 nanometers as a transmitter, the fast microchannel plate photomultiplier
tube along with an appropriate electric discriminator or an avalanche photodiode as a return
signal detector reaching _i time interval resolution of 30 picoseconds. An electronic time
interval unit having a resolution of 20-35 picoseconds is used to determine the interval
between the laser pulse transmittion and echo signal detection |.
The limiting factor for the current systems accuracy improvement from centimeter to
millimeter level are the currently used detectors and discriminators, time interval meters and
the contribution of the target itself. The main contributors to the systematic error and hence
limiting the final accuracy is the atmosphere. The existing atmospheric models based on
meteorological data permit to predict the atmospheric optical delay with centimeter accuracy.
It is expected, that ranging simultaneously on two wavelength and determining the two
wavelength propagation time difference, the existing atmospheric models will be improved
to millimeter accuracy. However, to obtain the valuable data for atmospheric model
improvement, the two wavelength delay must be measured with picosecond accuracy 2 .
The goals of the implementation of a streak camera into a laser ranging system :
The first : the replacement of the existing detectors and discriminators by the streak camera
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with and appropriate readout and data processing system. This will increase the time interval
resolution of the radar detection chain several times, the echo pulses distortion by the target
geometry may be monitored and compensated. The second : the streak camera will be used
for two wavelength laser ranging echo signals detection, the two wavelength range delay may
be determined with the picosecond accuracy. The third : along with the detector, the streak
camera may be integrated into the time interval unit. The picosecond time resolution and a
high overall timing accuracy is expected'.
THE STREAI_ CAMERA CONSTRUCTION
Designing the streak camera for satellite laser ranging purpose several key problems
have to be solved:
- the energy budget of the ranging chain, closely connected to the photocathode and sweep
speed used,
- the camera configuration, the type of deflection, input optics configuration,
- the readout system and the output data processing.
Completing the series of indoor and ground target ranging experiments, we have
chosen the $25 photocathode, the circular sweep camera setup and a two dimensional TV
readout system with a full frame image processing. The linear sweep tube setup reaches
higher limiting temporal resolution. However, the necessity of a trigger signal appearing 10-
30 nanoseconds prior to the photons to be detected with a subnanosecond jitter and the angu-
lar/temporal relation may cause serious difficulties when ranging to satellites. Using the
circular sweep tube setup, the trigger signal requirements are moderate • the trigger signal
must appear 10-20 microseconds before the optical signal, the jitter of several microseconds
is acceptable. The temporal/angular dependence may be monitored, software modelled and
compensated.
The PV-006 streak tube having the $25 photocathode and the microchannel plate
image intensifier fiber optically coupled together have been used. The streak tube is equipped
with two pairs of deflecting plates acting in the mutually perpendicular direction. Applying
the RF signal phase shifted to both deflection plate pairs, the circular sweep may be obtained.
The 320 MHz signal, 13 Watts of pulsed RF power is used. The maximal RF power ap-
plicable on the deflection system is limited by the internal ionization inside the tube. The
diameter of the circle was about 6 mm resulting in 155 psec/mm sweep speed. Due to the
imperfect impedance matching of the RF driving circuit to the tube deflection system, the
deflection is not perfectly circular. Nevertheless, the complex streak image processing and
calibration package is able to compensate for these effects. The temporal resolution of 30-35
psec and the range difference jitter 6 psec have been achieved.
The application of the streak camera for ranging purposes is accomplished by the timing
and gating circuitry. The deflection signal is ON for only few microseconds before laser
transmittion and again few microseconds before expected arrival of the satellite echo. All the
remaining time the camera is working in the static image mode and may be used for guiding
/ alignment purposes, as well. The 320MHz deflection signal is produced by multiplication
of the 5 MHz sine wave output of the station Cs beam frequency standard, which is simul-
taneously acting as an master oscillator for all the station timing electronics. This way, the
precise phase synchronism of the radar electronics and the camera circular deflection is
maintained. In fact, the camera may be used as a vernier to the time interval unit, rough time
interval is derived from the integer number of periods from Start to Stop event, the fraction
of the period may be determined from the phase difference of the Start and Stop events s.
The microchannel plate intensifier gain is controlled in three steps. During the laser
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transmittion, the gain is set to minimum to avoid the blinding of the system by the
atmospheric backscattered light. Optionally, the mechanical shutter in front of the input
photocathode is used. Most of the time the microehannel plate gain is set to 100, a com-
promise between the static image mode gain and the background noise contribution. At the
expected echo arrival time, the gain is set to maximum of 10,000 for 300 microseconds to
achieve maximum detection sensitivity.
To readout the tube screen image we use the Silicon Intensified Target (SIT) tube
made by Haimann. The output signal was fed to the Visionetics Frame Grabber card (512x51-
2x8bits) inserted in the IBM PC. To solve the problem of a deflection nonsymetry, the
software package 3 allows the full frame image processing and accomplishes the software
modelling of the image distortion, the sweep nonlinearity, the gain nonuniformity etc. On the
end of the image processing procedure the temporal curve consisting of 1000 channels, 8 bits
each is generated. Once the center of the deflection circle is identified, for example using the
satellite image in the static mode, the temporal/angular effecP may be software compensated.
The compact design of the camera, its rugged construction along with its low mass
permitted to install it directly on the moving part of the tracking telescope.
SATELLITE LASER RANGING SYSTEM
The streak camera has been integrated to the Satellite Ranging System of the
Lustbuehel Observatory, Graz, Austria. The ranging system consists of a modified Quantel
laser, passively mode locked NdYAG with the second harmonic generator, delivering pulses
of 10 milliJoules, 35 picoseconds in green. Alternatively the semitrain of 5 - 7 such pulses
containing totally 60 milliJoules may be transmitted. The telescope is a Contraves laser
tracking type. The laser output is transmitted by a 10 cm diameter Galileo telescope, the 0.5
meter diameter Cassegrain optics is used for both return photons collection and visual
guiding. The streak camera replaced an original ISIT camera attached to the telescope and
dedicated for faint objects visual tracking. The dielectric mirror is directing 99% of the
returned photons on the streak photocathode the remaining photons enter the standard detector
package based on a single photon avalanche photodiode. All the rest of the satellite laser
ranging hard/software remained unchanged. Thanks to the photodiode single photon response
capability, the satellite routine ranging capability has been preserved, although with reduced
return rate. The streak camera system timing and gating logic has been added.
The streak tube, the image intensifier and the readout have been kept at the
temperature + 5 C what resulted in significant dark noise reduction.
RESULTS
The retroreflectors equipped satellites at the distances of 1,000 to 2,300 kilometers
have been ranged. The first satellite laser ranging echoes recorded by a streak camera have
been obtained January 18,1991 at 21:37 UT from the AJISAI satellite at the distance 2000
km, see Figure 1. In this stage, the semitrain of pulses separated by 8.557 nanoseconds has
been transmitted. On the image the time interval of 40 milliseconds covering the laser pulse
transmittion to echo detection is integrated. The transmitted laser beam backscattered light
image is near the center of the pattern displayed in the static image. At this moment the
satellite was not illuminated by the Sun. On Figure 2 there is a streak camera record of the
AJISAI satellite echo obtained transmitting single picosecond pulse containing 10 mJ of
energy. The temporal profile of the firs part of the trace is included. Please, note the streak
camera receiver system saturation by the strong echo signal coming from the first rows of the
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corner reflectors. The satellite is a sphere of diameter exceeding two meters covered with
retroreflectors. According to numerical simulations, the returned pulse should be spread over
the time interval about one nanosecond depending on the satellite orientation. The separate
echoes coming from various retroreflectors may be clearly distinguished. The sweep speed
nonlinearity has not been compensated on this display. The central spot is an static image of
the satellite illuminated by the Sun, thus marking the center of the sweep. The atmospheric
backscattered light has been blocked out by the mechanical shutter. The STARLE'ITE
satellite echo record is on Figure 3. Single picosecond pulse has been transmitted. The
satellite is a sphere covered with retroreflectors of the diameter of about 25 centimeters at a
distance about 1,000 kilometers. The echo signal time spread is significantly smaller in
comparison to the AJISAI satellite. The temporal profile of the echo is included, as well. The
detector saturation may be seen. The system temporal resolution may be demonstrated on the
not saturated response from a single corner reflector resulting in a pulse width of 25-30
picoseconds.
CONCLUSION
The first satellite laser echoes have been recorded on the streak camera to our knowledge
for the first time. The applicability of a Modular Streak Camera system employing the
circular sweep for satellite laser ranging has been demonstrated. The sensitivity of the streak
camera has been confirmed to be satisfactory for the purpose : for standard geodetic satellite
ranging employing available laser ranging technology.
REFERENCES
1. J.J.Degnan, "Satellite Laser Ranging: Current Status and Future Prospects', IEEE
Trans.on Geoscience and Remote Sensing, Vol. GE-23,pp.398-413,July 1985
2. J.Abshire, Applied Optics, Vol. 19, No 20,pp.3436-3440, 1980
3. P.Valach," Streak Camera Full Frame Image Processing', proc.of the Seventh
International Workshop on Laser Ranging Instrumentation,Matera, Oct.1989, edited by
C. Veilet,CERGA,France
4. I.Prochazka, K.Hamal, "Streak Camera as a Laser Radar Receiver, its Performance and
Limitations', pro<:, of the Sixth International Workshop on Laser Ranging Instrumentation,
Antibes, Sept. 1986, edited by J.Gaignebet,Cerga,France, 1987
5. K.Hamal, I.Prochazka, M.Schelev, V.Lozovoi, V.Postovalov, " Modular Streak Camera
for Ranging', presented at the 19th International Congress on High Speed Photography and
Photonics, Cambridge, UK,Sept. 17-21,1991, published in SPIE 1358-55
5-50
SATELLITE LASER RANGING
FIRST STREAK RECORDS
O
AJISAI satellite, diameter 2., meters
range 1 500 km
January 19, 1991 , UT 21:37
4* V0
C=
• dk
sweep period 3.125 nsec, displayed part 1 nsec
Fig. 1
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i i m •
qk &
,,(Ik,
aeplitude AJISAI satellite picosecondlaser pulse responseon streak
125
188
?5
58
25
8
• mr
/
. ! ,J
8 68 121]
time [ 5 psec/pixel ; 1.5 nsec/screen ]
5-52 Fig. 2
SATELLITE LASER RANGING
FIRST STREAK RECORDS
STARLETTE satellite, diameter 0.3 meter
range 1 000 km
January 24, 1991 , UT 21:59
• f •
v
i_lnn _
100 psec
15 mm range
echo signal temporal profile 8 psec / pixel
Fig. 3
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Calibration
T ech niques/T argets



The first satellite laser echoes recorded on the streak camera

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