A dual field of view lidar system with two independent receivers is described to realize the detection of atmospheric aerosols. A CCD camera is attached to a backscatter lidar as a receiver to complement the data in the near-field range affected by the incomplete overlap between the laser beam and the receiver field of view. The signal detected by the CCD camera is corrected and finally glued with the signal of the backscatter lidar to retrieve the aerosol extinction coefficient with Fernald algorithm. The aerosol extinction profile and visibilities measured by the dual field of lidar had been compared with the results measured by another general backscatter lidar and a surface aerosol instrument, respectively. The results suggested that the dual field of view lidar based on a CCD camera is feasible and reliable. It could obtain the data both in the near and in the far range simultaneously, improving the detection accuracy of the lidar system effectively.

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Atmospheric Aerosols Detection Research with a Dual Field of View Lidar

Star trackers are beyond dispute the most accuracy absolute attitude determination sensors which are widely applied
in spacecraft, satellites, rockets, etc. High precision autonomous star tracker has accuracy better than one arc second and
generally resulting in a low update rate less than 10Hz. Typically, an autonomous star tracker consist two physically
independent components, the optical head and the associated processing electronic system. High accuracy attitude is
obtained through their cooperation. Basic principles of star navigation and components of a star tracker will be
introduced. Star trackers used to be with big body size, heavy mass, high power consumption and complicated structure but
with low accuracy. The state-of-the-art development will decrease the power consumption and mass of autonomous star
trackers significantly while increase update rate and improve dynamic accuracy and system robustness. Advance of
different generations of star trackers will be reviewed here. The accuracy performance of the star tracker depends on the
sensitivity to the starlight of the image sensor, the star detection threshold, the field of view (FOV), the number of stars in
the FOV, the accuracy of the star centroid, the dynamic maneuvering, the calibration and etc. Star centroid is a key
procedure and contributes much more to the final performance of a star track. Accuracy degradation will occur when the
carrier of the star track is in the state of high dynamic maneuvering. Hardware design and algorithms remedies have to
been adopted to reduce the degradation effects. Detailed discussion of accuracy performance will be presented.

Advances and accuracy performance of the star trackers

Space-based Space Target Detecting (SSTD) has great advantages than that of ground-based, so it is a necessary tendency to make efforts to develop this technology. This paper firstly analyses the effects on visible light imaging caused by the severely space environment, models the space-based image. After that, a new algorithm for target detecting and tracing is presented. Experiment results based on ground-measured data show that the performance of the algorithm are satisfying when the SNR of image sequences is greater than 4, and it has the capability of multi-target detecting and tracking.

Research on Space-Based Space Target Detecting and Tracking Algorithm

Ultraviolet (UV) sensors on a geostationary orbit (GEO) have important potential value in atmospheric remote sensing, but
the satellites orbit mode of it is quit different from sun-synchronous orbit satellites, which result in the significant diurnal
and seasonal variations in radiation environment of earth observation and radiation signal of sensors, therefore, the effect to
sensor radiometric performance, such as signal to noise ratio for atmospheric ultraviolet remote sensing caused by
variations of solar angle is significant in the performance design of sensors. The synthetic ultraviolet sensor is set at the
geostationary orbit, 36000 km away from the sea level of the Equator with 8.75 degree field of view, and the subsatellite
track point of which is located at 90 degrees east longitude and Equator. The Satellite scanning angles (SA) from 0 to 8.648
degree that cover the earth surface are selected corresponding to the 10 degrees equal interval view zenith angle, and the
SA from 8.648 to 8.785 degree cover the earth lamb 100 km far away from earth tangent point. Based on the MODTRAN4
model, on normal atmospheric conditions, the distributions of the UV upwelling radiance from surface or limb viewing
path of the earth could be simulated with the change of sun's right ascension. Moreover, the average signal to noise ratio to
the atmospheric sounding is obtained in different UV spectra using the Sensor signal to noise ratio model. The results show
that the thresholds range, tendency and shape of signal to noise ratio have a variety of features affected by variation of Sun
hour angles and declinations. These result and conclusions could contribute to performance design of UV sensors on the
geostationary orbit.

Analysis of signal to noise ratio for atmospheric ultraviolet remote sensing on geostationary orbit with variations of solar incident angles

High sensitivity and SNR are requested in lunar astronomical observation in order to get dark and
feeble objects. Scientific CCD Cameras used in lunar astronomical observation usually have following
characteristics: high quantum efficiency, wide spectral response, good photometric linearity and wide
dynamic range. However, extremely low readout noise is usually a key indicator of the camera. A CCD
camera, based on E2V's back-illuminated ultraviolet-enhanced scientific grade AIMO image sensor,
has been designed for lunar astronomical observation. Four major kinds of electrical optimal design are
presented in order to reduce the readout noise of the camera. The experiment result shows that: in the
200K pix/s of the pixel clock, the camera system gain is 1.83e-/ADU, and the readout noise is less than
6e-.

Development of low readout noise scientific CCD camera for lunar astronomical observation

Three primary kinds of noise in the astronomical CCD camera system were analyzed: photon noise,readout noise and dark current noise,etc.Then the SNR model under the low-light-level conditions is proposed and further the simplified models vs different exposure time are proposed.According to the different simplified models,two different noise dominant regions are specified,photon-noise dominant region and readoutnoise dominant region.In the interest of the higher SNR and detecting ability in the CCD image,the on-chip binning technology can be employed.The experiment result indicates that the SNR model and the simplified models which be proposed out in this paper is effective.Therefore,the different exposure strategy can be adopted to detect the targets in the images effectively under different application.

Chen Zeng-ping

Papers

Noise Analysis and the Study of SNR Model on the Astronomical CCD Camera