Telescope Field Of View Research Articles

Calculation of the overlap factor and correction of near-field signal of the off-axis lidar based on the Gaussian mode of laser beam

Based on the geometrical analysis, the near-field overlapping area shape of an off-axis laser lidar, which is formed by the telescope field of view and the laser distribution, is divided into three types, and the analytical formula for calculating the overlapping factor of off-axis lidar is given. According to the formula and the Gaussian distribution of the laser mode, the curve of the overlapping factor with the altitude of the Mie scattering lidar in our Laboratory is obtained. Using the curve, the lidar return signal under different weather conditions in Chengdu is corrected, based on which the return signal is retrieved by the Klett inversion method, and the curves of the atmospheric extinction coefficient varying with the altitude are obtained. The results show that the atmospheric extinction coefficient obtained by the correction method in the study is accordant with the practical weather condition.

The field of view and flux sensitivity of RATAN-600

The refined data on the diffraction scattering of RATAN-600 allowed the telescope field of view to be increased substantially at large elevations. Amethod, which can be used to reconstruct the parameters of the sources passing at angular distances fromthe beamaxis that are several dozen times greater than the half-power width of the beam, is analyzed. The knowledge about wide scattering of RATAN-600 allowed the noise from background radio sources at zenith to be reduced by one order of magnitude and flux sensitivity of the radio telescope to be increased by the same factor without resorting to two-dimensional mapping. Methods for cleaning one-dimensional records of the RZF survey are suggested that use model scans based on the data of the NVSS survey and MHAT filtering. The latter proved to be an especially efficient tool for suppressing sky noise and identifying sources in the central section of the survey. The flux sensitivity of RATAN-600 is estimated with new opportunities taken into account.

A 15° wide field of view imaging air Cherenkov telescope

Contemporary imaging air Cherenkov telescopes (IACT) for ground-based very high energy (VHE) gamma-ray astronomy have prime focus optical design. Typically, these telescopes have a (2–4)° wide field of view (FoV). They use F/0.7– F/1.2 optics and provide (3–10)′ resolution in the FoV. Generally, a well designed telescope that includes more than one optical element will offer some advantages not available in prime focus designs, such as a wider FoV, a more compact size, a higher and more homogeneous resolution and a lower degree of isochronous distortion of light rays focused onto the focal plane. Also, they allow monitoring the gamma-ray activity in a sizeable portion of the sky in a single observation. This would allow one to perform a sensitive all-sky survey in a relative short time. We present an F/0.8 15° wide FoV telescope design, which provides a high and near uniform resolution and low isochronous distortion across the entire FoV.

Raman lidar system for hydrogen gas detection

A Raman lidar system for detection of hydrogen gas has been developed. The lidar system consists of a pulsed Nd:YAG laser of wavelength 355 nm and a Newtonian telescope of aperture 212 mm. The system can detect hydrogen gas by either rotational or vibrational Raman backscatter up to a distance of 30 m in outdoor, daylight conditions. Furthermore, the system can perform two-dimensional mapping of the hydrogen gas distribution by spatial scanning of the laser beam within the telescope field of view.

Wide-field Adaptive Optics correction using a single rotating laser guide star

The problem of providing Adaptive Optics (AO) correction over a wide field of view is one that can be alleviated by using multiple conjugate AO (MCAO), or a low-altitude Laser Guide Star (LGS) that is projected to an altitude below any high layer turbulence. A low-altitude LGS can only sense wavefront distortions induced by low-altitude turbulence, which is dominated by a strong boundary layer at the ground. Sensing only the wavefront from this layer provides an AO system with a more spatially invariant performance over the telescope field of view at the expense of overall correction. An alternative method for measuring a ground-layer biased wavefront using a single rotating LGS is presented together with a numerical analysis of the wide-field performance of an AO system utilizing such a LGS. System performance in H and K bands is predicted in terms of system Strehl ratio, which shows that uniform correction can be obtained over fields of view of 200 arcsec in diameter. The simulations also show that the on-axis performance of a LGS utilizing Rayleigh backscattered light will be improved.

An adaptive 2 m class telescope for a microlensing search from Antarctica

We describe the scientific rationale and the preliminary optomechanical design for a 2 m class telescope designed to achieve ground layer correction over a ≈ 15 arcmin Field of View (FoV) to be located at the Dome-C site. The proposed science case is the detection of microlensing events in and by globular clusters and nearby galaxies that, for a high probability of success, requires exceptional seeing ( ≈ 0.2 arcsec or better) and a large target density (the centre of a globular cluster with a corresponding telescope FoV of ≈ 15 arcmin). This approach can capitalise on some of the unique qualities already observed above the Dome-C site, namely that the atmospheric turbulence is largely limited to a ground layer of small thickness only, a relatively low Greenwood frequency and uniterrupted sky coverage during the winter months for objects such as the globular cluster 47-Tuc. Further to the central science case of microlensing the telescope could provide a technological testbed for future telescopes and, given the unique atmospheric properties witnessed already during previous site testing compaigns, has the chance to provide a large amount of data (based on accurate and continuous light curves lasting several months) for fields of research outside that of microlensing. Details of the specific concepts of adaptive optics to be adopted for this telescope are outlined.

Activity science with data from the upcoming generation of space-based high-accuracy photometric data

A number of high-accuracy photometric missions will be launched in the next 6 years, starting with small, missions which will observe only a handful of objects and progressing to large size (1 m class), large field of view telescopes allowing the observation of up to some 100 000 stars simultaneously. While the prime science goals of these missions will be asteroseismology and terrestrial planet finding, their long-term, accurate photometric data will encode the surface activity pattern of each target star, and thus allow activity science to be performed on unbiased samples of stars of unprecedented size. The measurements which can be carried out in this way include the integrated activity level, the spot distribution and the rotation period. We discuss summarily the upcoming missions, and in some detail the activity measurements which can be performed with them. Eddington, an ESA mission whose primary science goals are asteroseismology and extra-solar terrestrial planet finding, and scheduled for launch in 2007, is also discussed in some detail.

Validation of a novel ultraviolet lidar system with relative Raman-scattering cross sections determined from atmospheric measurements.

We have developed an ultraviolet lidar system in which the upwelled laser beam and the telescope field of view can be made to overlap at any specified location in space. We refer to this system as the Selected Overlap Lidar Experiment. We discuss validation of our system by calculating relative Raman-scattering cross sections (with respect to the nitrogen scattering cross section) for oxygen and water vapor using data collected during field operations of our lidar. Our relative cross sections are consistent with those obtained by other researchers making similar measurements in laboratory environments.

Review of GRANAT observations of gamma-ray bursts

The GRANAT observatory was launched into a high apogee orbit on 1 December, 1989. Three instruments onboard GRANAT - PHEBUS, WATCH and SIGMA are able to detect gamma-ray bursts in a very broad energy range from 6 keV up to 100 MeV. Over 250 gamma-ray bursts were detected. We discuss the results of the observations of the time histories and spectral evolution of the detected events provided by the different instruments in different energy ranges. Short Gamma-Ray Bursts ( 2 s) events. Evidence of the existence of four differently behaving componenents in gamma-ray burst spectra is discussed. Statistical properties of the gamma-ray burst sources based on the 5 years of observations with (∼ 10−6 erg/cm2) sensitivity as well as the results of high sensitivity (∼ 10−8 erg/cm2) search for Gamma-Ray Bursts within the SIGMA telescope field of view are reviewed.

Design Of A Wide Field Of View Phased Array Telescope

The design of the Multipurpose Multiple Telescope Testbed (MMTT) is described. The MMTT, whose construction is now nearly complete, is believed to be the first wide field of view phased array imaging telescope. The design philosophy and alignment requirements are discussed and the telescope is described. The array consists of four 20 cm telescopes and operates with visible light. The coherently combined image has a 30 arcmin field of view. A key design goal is the maintenance of lateral pupil geometry to within 1µm of the ideal. Two mirrors behind each afocal telescope combine the four beams into one and are actuated to control both tilt and piston. Together, the two beam combiner mirrors control lateral pupil geometry. A control system senses the lateral pupil geometry error by continuously measuring piston phase changes over the telescope field of view. A discrete time varying Kalman filter then processes these measurements to estimate lateral pupil geometry errors.

Mount Wilson Telescope to be mothballed

As part of its plan to direct resources to its astronomical research facilities in Chile, the Carnegie Institution of Washington will mothball the Mount Wilson 2.54‐m telescope on July 1, 1985, and will gradually decrease support for the 45.7‐m and 18.3‐m solar tower telescopes. Concurrently, the Mount Wilson and Las Campanas Observatories' technical development group in Pasadena, Calif., will be expanded.New equipment will be acquired for the Las Campanas Observatory in Chile, where Carnegie operates two modern telescopes. A charged coupled device camera will be added to the 1.0‐m telescope at the observatory to yield more accurate imaging of extremely faint objects. Another charged coupled device will enable the recording of spectra of extended sources, including galaxies and emitting clouds. Eventually, this device will permit fiber‐optical feeds for the simultaneous recording of many objects in a group of stars or galaxies. Also on the list is a new spectrograph that will introduce high‐resolution spectroscopy for the first time at the Las Campanas Observatory's 2.54‐m telescope. Computer facilities at the observatory will be upgraded. In addition, improvements will be made for the television viewing systems that aid in locating faint sources in the telescope field of view.