General Introduction

This observatory is located inside a National Park of 76,000 Hectares (almost 200,000 acres) which has the status of Protected Astronomical Reserve (PAR).

The eastern part is bounded by the Tontal mountains, reaching a peak altitude of 4200m, while the western boundary is set by the provincial route RP 412.

 

 

To see more details on the surveyed area click on the map Casleo map

The Andes ridge rises a few kilometres westwards of RP 412. At this geographical latitude there are several high altitude peaks (Mercedario 6,770m and Aconcagua 6,956m, among others). Within the PAR there are numerous plateaux that are separated from each other by low altitude chains of peaks stretched along a north-south direction. This particular orography provides additional shielding against potentially harmful man-made signals.

Among the plains it is worth mentioning Pampa de la Ciénaga del Medio (6 km x 3 km, figure in the left), Pampa del Peñasco (8 km x 6 km), Pampa del Jarillal (15 km x 6 km), and Pampa de las Cabeceras (11 km x 3.5 km). The quoted dimensions correspond to (north-south x east-west). The first two are almost flat whilst the last two have a mild slope along an east-west direction.

Atmospheric opacity determinations at CASLEO at 212 and 405 GHz are routinely determined by the Solar Submillimeter Telescope. Recent results spanning the period March 2002- February 2003 indicate that the most probable value for zenith opacities is 0.27 nepers at 212 GHz and that 56% of the time the opacity is lower than 0.3 nepers. (A.A. Melo et al., 2004). The precipitable water vapor (pwv) content of the atmosphere above CASLEO varies between 3 to 5 mm with a small seasonal variation. This low content of pwv may be an advantage for observations at the high frequency extreme of the proposed total frequency tuning range of the SKA.

By Provincial Law No. 5771 (approved by San Juan's Legislative Power on October 1st, 1987) the entire Astronomical Reserve is protected against harmful effects caused by both light and radiofrequency pollution.

Bearing in mind the relatively clean radiofrequency environment found in CASLEO, more sensitive RFI meassurements are planned in the area for next Winter, specially in a plain at 3200 m of altitude (Pampa del Jarillal) located 13 km east of the position listed in Table 1 (see main page).

CASLEO is linked to the national energy network by means of a threephase 13.2 kV line.

Road Access

This site can be accessed from north by provincial route RP 412. This route originates in San Juan City (located 180 km north-east from the site). At present this road is mostly paved, and will be completely paved till the detour that marks the entrance to the PAR by January 2005. From there, 17 km of good but unpaved road follows.

From south (Mendoza City) the site can be accessed by national route RN 7. This route links Argentina and Chile and is an all-weather road till Uspallata (105 km northwest of Mendoza City). The remaining 93 km till the site entrance is a good unpaved road.

Air Access

No air traffic routes are allowed above the Astronomical Reserve. South of the site, Mendoza City international airport (1 hour fly-time from the City of Buenos Aires) is very well suited for accommodating large cargo aircrafts. This airport is served by several national and international carriers. On the other hand, north of the site we find San Juan airport, served by national carriers (Aerolíneas Argentinas - Austral) twice a day. Direct fly-time from Buenos Aires airport to San Juan is around 1.5 hours, while the fly-time from Mendoza to San Juan is about 45 minutes.

After obtaining special permit from either San Juan or Mendoza airport authorities, a light aircraft could land in the proximity of the junction of RP 412 and the road leading to CASLEO.

Population density, nearest towns and major urban centers

Being a Protected Astronomical Reserve, there are no settlements within its borders. The nearest towns are Barreal (17 km away in straight line) and Calingasta (44 km) with a population of 3200 and 2040 inhabitants, respectively.

As regards to major urban conglomerates, the fourth largest city of Argentina (Mendoza City with a population close to 1 million inhabitants) is located 215 km south of CASLEO. Towards the north, San Juan city, with its 120.000 inhabitants, is the closest major urban center.

Licensed Broadcast Transmitters

There are no broadcasters within a circle of radius 15 km centered at the location of the 2.15m optical telescope (Provincial Law 5171). Two AM and one FM (90.0 MHz) low-power radios are based in Barreal. Due to the extra shielding provided by the local topography, these radios can only occasionally be tuned at CASLEO. A TV (channel 8 from San Juan) relay station, that serves Barreal, is located 25 km north of the observatory.

Geological characterization and Seismic Activity

The site is in the Precordillera Region. It is a mountainous region in which Early and Middle Paleozoic deposits with an important fosiliferous content prevail. Limestone, dolomitic limestone and shales are frequent rocks. The sedimentites are folded and they have strong dips. The tectonic movement (faulting) produced the rise of the region and at present it is still manifested.

The seismic activity in this area is of some importance. Based on the Advanced National Seismic System catalog, within a circle of radius 100 km centered at the CASLEO 2.15m optical telescope, twenty-one (21) earthquakes with intensity magnitude superior to 5 were registered during the last 10 years. The average depth of their epicenter is 102.3 km. For comparison, the same search restrictions for first-rank optical observatories installed in Chile, like Cerro Tololo Inter-American Observatory (CTIO) and the European Southern Observatory (ESO), yield thirty-one (31) earthquakes for the CTIO site and nineteen (19) for the ESO site. In these cases the mean epicenter depths are 50.8 (CTIO) and 35.6 km (ESO), respectively. A similar comparison can be done with the planned Atacama Large Millimeter Array (ALMA) site, in northern Chile. In this case, thirteen (13) earthquakes took place during the last ten years. The mean epicenter depth is 125.9 km and four (4) of them had an epicenter depth in the range from 11.7 to 33 km. Using the information gathered from the national network of accelerometers installed by the Instituto Nacional de Prevención Sísmica all over the country the maximum acceleration likely to occur in San Juan (within a recurrency period of 50 years) is 2.1 m/seg2.

Summing up, though seismic activity is present in the area, it seems to be similar to the one present in other places where large observing astronomical facilities are operating or will be installed in a near future.

Though addmittedly the RFI measurements, due to logistic limitations, were not conducted at the best possible location within the Protected Astronomical Reserve (see RFI Report - Site Measurements), it is important to note that even in this condition the peak RFI signals achieve a maximum spectral flux density (SFD) of -166 dBW m-2 Hz-1 at frequencies above 50 MHz. Around 50 MHz, mean floor levels of -180 dBW m-2 Hz-1 are usually found.
A typical RFI spectrum in the frequency range 50 to 200 MHz at CASLEO. This spectrum is the result of integrating 70 minutes using a low gain biconic antenna directed at azimuth 315o and elevation 0o with horizontal polarization.

In the frequency range from 200 to 1100 MHz, most of the band is free from interferences. The strongest signals detected in this spectrum are originated within the observatory itself. From one extreme of the band to the other, the noise floor increases by 22 dBW m-2 Hz-1 as a result of changes in the antenna effective area and cable attenuation variation with frequency. As mentioned above the strong signals at 218.9, 459.2, 459.4, 459.8 and 481.7 MHz arise from local phone links. Due to their local origin, migration from microwave links to optical fibre may be a way of wiping out these harmful signals.

Plot of RFI measurements in the range 200 to 1100 MHz. The strongest signals are man-made ones (see text). This spectrum was taken with vertical polarization towards azimuth 22o and elevation 0o. The total integration time is 110 minutes.

  At the high frequency band (1100 - 3000 MHz) no attempt was made to calibrate the gain of the antenna and the plots are given in units of dBm. The spectrum is almost featureless. The only signal present is a spike at 2,415 MHz resulting from an internet microwave link between CASLEO and a relay station located 25 km north of the observatory. This signal is highly directional.
Plot of RFI measurements in the range 1100 to 3000 MHz. The strongest signal detected in horizontal polarization towards azimuth 0o (red line) is the fingerprint of an internet link me (see text). The integration time is 70 minutes. The spectrum depicted in blue was taken towards azimuth 345o and the link signal is missing. The integration time at azimuth 345o is 140 minutes.

 


2004 - SKA Argentine Committee