Power Spectral Density (PSD) is an alternative method for specifying optical surfaces, and quantifies the contribution of
each spatial regime to the total surface error. This approach naturally includes mid-range spatial frequency errors, which
are often overlooked. The PSD method has recently been adopted by the Space and Astronomy industries, but has not yet
received general acceptance within the synchrotron community. To assess the suitability for specifying synchrotron
optics using PSD, Fast Fourier Transforms were performed on topography data from a range of optical surfaces of
varying quality and manufacturing techniques. For each grade of optic, the entire regime (~100nm to ~50mm) of surface
errors was measured, with overlapping bandwidths, using a micro-interferometer and a Fizeau interferometer. From this
heuristic information, root-mean square "roughness" can be predicted over any desired spatial range, thus allowing direct
comparison of metrology data obtained by instruments with different spatial bandwidths. We present an efficient
approach for calculating 1-D and 2-D PSDs using MATLAB algorithms, and discuss analysis considerations, including
"field of view" effects and instrument calibration.
A laser Fizeau interferometer system has been developed to characterize the figure error of large synchrotron X-ray
mirrors using double-pass geometry. This opto-mechanical assembly comprises integrated rotation and translation stages
to control: the output angle of the Fizeau interferometer; the surface normal of the optic under test; and the orientation of
a high quality (λ/100) retro-reflector. To negate the effects of gravitational deformations, the system can measure long
optics (up to 1.5m in length) in the geometry (sideward, downward, or upward facing) in which they will ultimately be
used on a synchrotron beamline. The system has been designed to minimize environmental noise and enable the
measurement geometry to be changed quickly and safely. Compared to complementary techniques, including slope
profilers such as the Diamond-NOM, surface height data from the Fizeau system can be obtained more rapidly (<1
minute). This makes the technique ideally suited to investigate the many degrees of freedom of adaptive optics, including
piezo bimorph mirrors. The shape of such optics can also be monitored in real time to observe the dynamic effects of the
surface in response to applied voltages. Results are presented to illustrate system performance, including repeatability
levels. Calibration of the reference surfaces and the required environmental conditions are also discussed.
A Fizeau interferometer based system has been developed to measure the figure error of
large synchrotron optics using single-pass, double-pass, and stitching geometries. The
system, which uses a λ/100 reference flat, is designed to measure optics up to 1.5m in
length, and is capable of nanometer level repeatability. Fizeau measurements, in single
pass geometry, are conventionally limited to the diameter of the laser beam, typically
150mm or 300mm. Stitching adjacent fields of view together or using a double-pass
geometry, allows much larger optics to be characterized. Results for the single-pass,
double-pass, and stitching geometries are shown to give consistent figure error values.
Data is also in good agreement with an autocollimator-based slope profiler. The Fizeau
method is also advantageous since data can be acquired in less than 1 minute, particularly
useful for characterizing the many degrees of freedom of active or adaptive optics. To
obtain results consistent with alternative techniques, the importance of an a priori
knowledge of the surface topography of the reference optics is also demonstrated.
This work overviews recent advances that have been made in an analytical theory of elastic and Raman lidar returns with multiple scattering and polarization from clouds and seawaters and outlines newly developed software for computer simulation of airborne oceanic lidar performance.
The feasibility of retrieving information from lidar return signals has been discussed in connection with salient features of the formation of multiple scattering for different lidar field-of-view angles (FOVA). However, the aspects of hydrosol sensing connected with the presence of the rough air-water interface make the lidar signal interpretation more difficult. Results of a statistical simulation by the Monte Carlo method are presented in the report for a water scattering layer homogeneous with depth. peculiarities of the waveforms of the lidar signals recorded during a flight above Lake Baikal (in November 1996) and the Atlantic Ocean to the West of Great Britain (in June 1997) are discussed. We estimate that the effect of multiple scattering compensates for the effect of wind-driven sea waves when FOV angle is about p/2 equals 3 - 4 mrad, and that these FOVA are optimal for sounding.
Experiments with a blue-green laser radar system were conducted off the coasts of Ireland and Scotland in June, 1999. The purpose of this test was to measure the effect of the water optical properties on the polarization state and decay rate of the lidar return signal. The lidar system, the K-meter Survey System (KSS), was configured to transmit linearly polarized light and to receive cross-polarized light in one channel and both polarization in the other channel. Several oceanographic ground truth instruments were used to measure the water optical properties, including transmission, absorption, backscatter coefficient, diffuse attenuation, temperature and salinity, as a function of depth. The KSS was mounted on the bow of one of the UK survey vessels, the HMS Roebuck, and the oceanographic instruments were deployed with a deck-mounted winch. The results presented in this paper were obtained both inside and outside of the continental shelf. Since these regions were characterized by different water optical properties, the sensitivity of the lidar return signal in terms of decay rate and polarization to different water clarities was determined.
The results of experiment on airborne laser sounding of coastal sea waters about Northern Scotland are described. The aircraft- laboratory of Institute of Atmospheric optics with Makrel-2 lidar was used. As a rule, the flights were carried out at height 300 M above water with average speed of 320 km/h. The pulse repetition rate of laser shots changed from 5 up to 25 Hz. The total length of flight lines above water surface has made about 8000 km. The processing of signals was made by a method of logarithmic derivative with statistical processing. The large attention was given to neutralization of influence of afterpulses, arising in photomultipliers, and especially strongly interfering to sounding of water.
Lidars are widely used for sensing of sea water turbidity and bottom depth. Our Makrel'-2 lidar has been used since the 1980s for water monitoring and searching for schools of fish over the Norwegian, Barents, and North seas. In the present paper, we discuss the results obtained with our lidar, placed onboard the Optik-E Antonov-30 aircraft- laboratory during our flight over Lake Baikal on November 2, 1996. Some results of lidar data processing are presented, which demonstrate the salient features of lidar return signals and the possibilities for lidar signal processing. The extinction index of the purest water found in the northern part of Lake Baikal was 0.12MINPLU0.01 m- (averaged over 600 pulses). In the region near the mouth of the River Selenga, the extinction index changed from 0.14 to 0.6 m-. The minimum and maximum bottom depths recorded with our lidar are estimated. We detected bottom depths as great as 40 m when the aircraft flew near Bol'shoi Ushkanii Island.
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