The multi purpose UV-Vis. Spectrometer for Atmospheric Tracers Measurement (SPATRAM) is installed at the
Observatory of the Geophysics Centre of Evora (38.5º N, 7.9º W) - Portugal, since 2004, measuring the zenith scattered
radiation in the 300-550 nm spectral range. The main products are the total column and the vertical profiles of NO<sub>2</sub> and
O3 obtained with the application of the Differential Optical Absorption Spectroscopy (DOAS) algorithms and with
inversion schemes based on the Optimal Estimation methods respectively. Recently (February 2009), the MIGE
(Multiple Input Geometry Equipment) was coupled to the SPATRAM instrument allowing for the measurements of the
diffused radiation in directions away from the zenith one (Off-Axis). MIGE is an alt-azimuth platform based on a very
simple optical layout, using an optical fibre to transmit the radiation inside the monochromator of the SPATRAM
equipment. Thanks to the solution adopted in the developing phase, MIGE is able to scan the whole hemisphere. In this
work, after a brief description of the MIGE, the first and preliminary results for vertical profiles of NO<sub>2</sub> in the Planetary
Boundary Layer (PBL), and the values of Slant Column Densities (SCD) of O<sub>3</sub> and SO<sub>2</sub> measured in Off-Axis
configuration at Evora Station, are presented and discussed.
In this paper we present a methodology for the retrieval of the vertical profile of atmospheric gas pollutants in the
boundary layer from ground based remote sensing measurements. Nitrogen dioxide (NO<sub>2</sub>) and ozone (O<sub>3</sub>) slant column
amounts have been obtained with the Differential Optical Absorption Spectroscopy (DOAS) technique used in the
multiple axis configuration (the so called MAX-DOAS). The measurements have been carried out in the Presidential
Estate at Castel Porziano (Rome) in the period from September to November 2006 in the frame of a programme started
in 1994 for studying and monitoring the Estate's environment. The retrieval of information on the vertical profile of trace
gases from their slant column amounts requires: (1) the simulation of the radiative transfer in the atmosphere for Air
Mass Factor (AMF) calculation; (2) the application of inversion schemes. In this paper the vertical profiles of NO<sub>2</sub> and
O<sub>3</sub> obtained from multiple axis DOAS measurements and their daily evolution are presented and discussed. The day
under study is the 29th of October, 2006.
LIDAR (LIght Detection and Ranging) is an optical active remote sensing technology with many applications in
atmospheric physics. Modelling of LIDAR measurements appears useful approach for evaluating the effects of various
environmental variables and scenarios as well as of different measurement geometries and instrumental characteristics.
In this regard a Monte Carlo simulation model can provide a reliable answer to these important requirements. A
semianalytic Monte Carlo code for modelling LIDAR measurements has been developed at ISAC-CNR. The
backscattered laser signal detected by the LIDAR system is calculated in the code taking into account the contributions
due to the main atmospheric molecular constituents and aerosol particles through processes of single and multiple
scattering. The contributions by molecular absorption, ground and clouds reflection are evaluated too. The code can
perform simulations of both monostatic and bistatic LIDAR systems. To enhance the efficiency of the Monte Carlo
simulation, analytical estimates and expected value calculations are performed. Artificial devices (such as forced
collision, local forced collision, splitting and russian roulette) are moreover foreseen by the code, which can enable the
user to drastically reduce the variance of the calculation.
REMIR is the NIR camera of the automatic REM (Rapid Eye Mount) Telescope located at ESO-La Silla Observatory (Chile) and dedicated to monitor the afterglow of Gamma Ray Burst events. During the last two years, the REMIR camera went through a series of cryogenics problems, due to the bad functioning of the Leybold cryocooler Polar SC7. Since we were unable to reach with Leybold for a diagnosis and a solution for such failures, we were forced to change drastically the cryogenics of REMIR, going from cryocooler to LN2: we adopted an <i>ad-hoc</i> modified Continuous Flow Cryostat, a cryogenics system developed by ESO and extensively used in ESO instrumentation, which main characteristic is that the LN2 vessel is separated from the cryostat, allowing a greater LN2 tank, then really improving the hold time. In this paper we report the details and results of this operation.
REMIR is the NIR camera of the automatic REM (Rapid Eye Mount) Telescope located at ESO La Silla Observatory -
Chile and dedicated to monitor the afterglow of Gamma Ray Burst events. The REMIR camera is composed by a set of
sub systems: the array controller, the cooling system, the temperature and the pressure monitors, the filter wheel
controller, the dither wedge controller. During 2005, a complete re-writing of the REMIR software control system started
in order to optimize the system performances: the new configuration will adopt a client server architecture, where a
supervisor system accepts via socket the data acquisition queries from AQUA (the acquisition data suite), manages the
several components of the camera and the communication with the telescope control system. Here we describe in
particular the philosophy adopted to realize the general control system, the sub systems and the communication
During the early Summer 2003, the REM telescope has been installed at La Silla, together with the near infrared camera REM-IR and the optical spectrograph. ROSS. The REM project is a fully automated instrument to follow-up Gamma Ray Burst, triggered mainly by satellites, such as HETE II, INTEGRAL, AGILE and SWIFT. REM-IR will perform high efficiency imaging of the prompt infrared afterglow of GRB and, together with the optical spectrograph ROSS, will cover simultaneously a wide wavelength range, allowing a better understanding of the intriguing scientific case of GRB.
In this paper we present the result of the commissioning phase of the near infrared camera REM-IR, lasted for an extended period of time and currently under the final fine tuning.
The REM Observatory, recently installed and commissioned at la Silla Observatory Chile, is the first moderate aperture robotic telescope able to cover simultaneously the visible-NIR (0.45-2.3 microns) wavelength range. His very fast pointing and his full robotization makes it an ideal observing facility for fast transients. The high throughput Infrared Camera and the Visible imaging spectrograph simultaneously fed by a dichroic allows to collect high S/N data in an unprecedented large spectral range on a telescope of this size. The REM observatory is an example of a versatile and agile facility necessary complement to large telescopes in fileds in which rapid response and/or target pre-screening are necessary. We give in this paper an overview of the Observatory and its performances with emphasis to the innovative technical solution adopted to reach such performances.
Fast ground based simultaneous optical-near infrared observation of gamma-ray bursts (GRBs) is a mandatory priority to understand the physical mechanisms at work in these objects. The REM (Rapid Eye Mount) telescope, recently installed at La Silla (ESO, Chile), is an example of a new generation of small robotic telescopes having the capability to allow simultaneous optical and near infrared photometry and low resolution spectroscopy. The REM Optical Slitless Spectrograph (ROSS) is the optical instrument mounted on REM. ROSS has been attached, in one of the two Nasmyth foci, orthogonally to the optical axis and receives the optical light deflected by a beam splitter (dichroic), which leaves the infrared beam to continue along the optical axis where the infrared camera (REM-IR) is installed. Low resolution optical spectroscopy is obtained using an Amici prism mounted on the same filter wheel where are also mounted the broad-band V, R, I photometric filters. The detector head is a commercial camera hosting a Marconi 1024×1024 CCD chip.
We present the near infrared camera REM-IR that will operate aboard the REM telescope, intended as a fully automated instrument to follow-up Gamma Ray Burst, triggered mainly by satellites, such as HETE II, INTEGRAL, AGILE and SWIFT. REM-IR will perform high efficiency imaging of the prompt infrared afterglow of GRB and, together with the optical spectrograph ROSS, will cover simultaneously a wide wavelength range, allowing a better understanding of the intriguing scientific case of GRB. Due to the scientific and technological requirements of the REM project, some innovative solutions has been adopted in REM-IR.
Observations of the prompt afterglow of Gamma Ray Burst events are unanimously considered of paramount importance for GRB science and cosmology. Such observations at NIR wavelengths are even more promising allowing one to monitor high-z Ly-α absorbed bursts as well as events occurring in dusty star-forming regions. In these pages we present REM (Rapid Eye Mount), a fully robotized fast slewing telescope equipped with a high throughput NIR (Z, J, H, K) camera dedicated to detecting the prompt IR afterglow. REM can discover objects at extremely high redshift and trigger large telescopes to observe them. The REM telescope will simultaneously feed ROSS (REM Optical Slitless spectrograph) via a dichroic. ROSS will intensively monitor the prompt optical continuum of GRB afterglows. The synergy between the REM-IR camera and the Ross spectrograph makes REM a powerful observing tool for any kind of fast transient phenomena. Beside its ambitious scientific goals, REM is also technically challenging since it represent the first attempt to locate a NIR camera on a small telescope providing, with ROSS, unprecedented simultaneous wavelength coverage on a telescope of this size.
We describe the analysis of BeppoSAX gamma-ray burst monitor on-ground calibrations performed after the full integration of the spacecraft in order to explore in detail the dependence of the detectors efficiency on the direction and energy of impinging photons. Analytical techniques have been used to determine with reasonable accuracy this function by fitting the angular response at different calibration energies with simple models partially derived from the underlying physics and partially semiempirical. Satisfactory results have been obtained for the two detectors which have almost clean field of view and are co-aligned with the wide field cameras. Work is still in progress for the others. Preliminary results of ground calibration analysis have been already used to derive spectral information on gamma-ray bursts impinging parallel to the axis of the two best performing shields.
The Italian-Dutch satellite for x-ray astronomy BeppoSAX is successfully operating on a 600 km equatorial orbit since May 1996. We present here the in-flight performances of the gamma ray burst monitor experiment during its first year of operation. The GRBM is the secondary function of the four CsI(Na) slabs primarily operating as an active anticoincidence of the PDS hard x-ray experiment. It has a geometric area of about 400 cm<SUP>2</SUP> but, due to its location in the core of the satellite its effective area is dependent on the energy and direction of the impinging photons. A dedicated electronics allows to trigger on cosmic gamma-ray bursts. When the trigger condition is satisfied the light curve of the event is recorded from 8 s before to 98 s after the trigger time, with a maximum time resolution of 0.48 ms, in an energy band of 40 - 700 keV. As an instrument housekeeping the 1 s event ratemeter of the same detectors in the same energy band is stored regardless the trigger condition, allowing for an off- line detection of non-triggered events. Finally, the onboard software collects the event count rate that is used as anticoincidence, i.e. the events above a given energy threshold, typically kept at 100 keV. The flight-data screening is in progress, in order to extract real gamma ray bursts from the many sources of background. Already many results have been obtained, as those GRBs detected simultaneously with the wide field cameras oinboard BeppoSAX itself.
The phoswich detection system (PDS) is one of the four narrow field experiments on board the x-ray astronomy satellite BeppoSAX. PDS is devoted to deep temporal and spectral studies of celestial x-ray sources in the 15 - 300 keV energy band. It also includes a gamma-ray burst monitor. In this paper we compare the expected and observed in-flight performances. Our estimate of systematic errors in the background subtraction and in the spectral reconstruction are also presented and discussed.
The gamma ray burst monitor onboard the BeppoSAX satellite is a secondary function of the anticoincidence shields of the phoswich detection system hard x-ray experiment. For this reason the four CsI slabs operating as gamma ray bursts detectors have a not uniformly clear field of view. Actually the other SAX experiments partially obstruct the GRBM FOV in a way that strongly depends both on direction and energy. This peculiarity makes very hard to build-up a real response matrix of the experiment by simply interpolating the on-ground calibration. Therefore a complex activity of Monte Carlo simulation has been started using the MCNP code, in which the entire SAX satellite is described in a 3D geometrical reconstruction. This code is being used for the simulation of the on-ground calibration set-up, and once a good level of confidence is reached on that, it will be used to reconstruct direction, intensity and spectrum of the cosmic gamma ray bursts. In this paper we present the Monte Carlo set-up, discussing the approach to the work and the approximations that need to be done. Then the first results of the simulations are shown and compared, for some monochromatic energies and for several incoming directions, to the results obtained during the on-ground calibrations.