Future large and extremely large ground-based telescopes will demand stable geological settings.Remote sensing could
be an unvaluable tool to analyse the impact of geological activity at selected astronomical sites, namely the observatories
of El Teide (Tenerife, Canary Islands), Roque de los Muchachos (La Palma, Canary Islands), Mauna Kea (Hawaii) and
Paranal (Chile) and the candidate site of Cerro Ventarrones (Chile). In this sense, the extent of lava flows, eruptive
clouds or ground deformation associated to seismic and/or volcanic activity could be analysed and characterised through
Measurements of ground displacement have been carried out on the entire active volcanic island of Tenerife, Canary
Islands, by means of classical and advanced DInSAR techniques. The main limiting factor on the accuracy of DInSAR
measurements is the distribution of the water vapour in the lower troposphere. Hence, it is yet necessary to perform a
detailed spatial and temporal characterization of water vapour to understand, and to be able to carry out a direct
computation of, the effect of the tropospheric delay on DInSAR results. In this sense, satellite and balloon data have
been analysed to infer the variability in the distribution of water vapour and hence, the robustness of DInSAR results on
the island of Tenerife.
The development of adaptive optics systems for projects related to large telescopes demands a proper knowledge of the
atmospheric turbulence. Due to the lack of long-term information on optical turbulence, high-altitude winds (in particular
winds at the 200-mbar pressure level) were adopted as a parameter for estimating the total turbulence at a particular site,
since there are large wind databases spanning for several decades. On-site measurements of C<sub>N</sub><sup>2</sup>(h) profiles (more than 20200 turbulence profiles) from G-SCIDAR observations and wind vertical profiles from balloons have been used tocalculate the seeing, the isoplanatic angle and the coherence time for the Teide Observatory (Canary Islands, Spain). The connection of these parameters to wind speeds at ground and 200-mbar pressure level have been studied and discussed.
The requirements for current large and future extremely large telescopes as well as the quick development of IR
instrumentation demand a proper characterization of precipitable water vapour (PWV) above astronomical sites. A
comparison of PWV estimations from a photometer and a GPS (Global Positioning System) above the Observatorio del
Roque de los Muchachos (ORM, La Palma, Canary Islands, Spain) was carried out and it was found a linear relation
between both measurements. Such relationship will allow the calibration of the GPS measurements recorded at ORM for
the period June 2001- December 2008. These large time series of PWV estimations from GPS were used to perform a
statistical analysis of water vapour content above this astronomical site. Average annual value of night-time PWV of
4.86 mm was found. It was also found a clear seasonal behavior of the PWV above ORM, with smaller water-vapour
columns during winter nights (average 3.36 mm). The largest values of PWV are reached in the summer nights (average
6.75 mm). The data indicate that a significant percentage of nights (~38%) are well suited for thermal infrared
observations (with PWV < 3 mm), and 71% of nights present a "fair" or better IR observation opportunity at ORM.
Seismicity induces ground vertical and horizontal displacements that could affect the image quality obtained by
telescopes in a similar fashion than atmospheric turbulence. In this work, we study the effect of local seismicity relative
to atmospheric turbulence upon the image quality of astronomical observations at El Teide observatory, Canary Islands.
Three different aspects of seismicity are studied, namely regional seismicity (that is compared with other astronomical
sites), seismic noise and possible resonances between seismic noise and the structure of telescopes.
The infrared sky quality is an important parameter to take into account for the evaluation of astronomical sites. The traditional idea of considering higher altitude sites as better for infrared astronomical observations than sites at lower altitudes is not in agreement with observational data. It has been shown that the observational infrared spectrum at the Observatorio del Teide (OT) at an altitude of 2400m on the island of Tenerife (Spain) is similar to that expected for a site at the altitude of Mauna Kea (4100m) in Hawaii (USA). This result suggests that other parameters besides site altitude is playing an important role in determining the quality of a particular location for infrared astronomical observations. In this paper, we propose the troposphere thickness as one of the parameters that determine the suitability and quality of an astronomical site for infrared observations. The tropopause altitude defines the tropospheric thickness and hence, we present in this paper a statistical study of the tropopause layer altitude for four different astronomical sites. The results presented in this work suggest that the infrared quality at La Palma, La Silla and Mauna Kea could be similar in some epochs of the year, although they are located at different altitudes above the sea level. Mauna Kea presents the
thinnest troposphere during Summer and Autumn among the four studied sites, whereas La Palma exhibits the lowest altitude of the tropopause in Winter and Spring. Paranal presents most of the
time the thickest troposphere, suggesting worse infrared conditions for astronomical observations (based only in the thickness parameter) at this site, when compared to the other three in study.