Examinando por Autor "Sam, Lydia"

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Acceso Abierto
Quantifying the Congruence between Air and Land Surface Temperatures for Various Climatic and Elevation Zones of Western Himalaya
(Multidisciplinary Digital Publishing Institute (MDPI), 2019-12-04) Singh, S.; Bhardwaj, Anshuman; Singh, A.; Sam, Lydia; Shekhar, M.; Martín Torres, Javier; Zorzano, María-Paz; Martín Torres, J. [0000-0001-6479-2236]; Shingh, S. [0000-0003-4304-388X]; Zorzano, M. P. [0000-0002-4492-9650]; Sam, L. [0000-0003-3181-2960]; Bhardwaj, A. [0000-0002-2502-6384]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
The surface and near-surface air temperature observations are primary data for glacio-hydro-climatological studies. The in situ air temperature (T-a) observations require intense logistic and financial investments, making it sparse and fragmented particularly in remote and extreme environments. The temperatures in Himalaya are controlled by a complex system driven by topography, seasons, and cryosphere which further makes it difficult to record or predict its spatial heterogeneity. In this regard, finding a way to fill the observational spatiotemporal gaps in data becomes more crucial. Here, we show the comparison of T-a recorded at 11 high altitude stations in Western Himalaya with their respective land surface temperatures (T-s) recorded by Moderate Resolution Imagining Spectroradiometer (MODIS) Aqua and Terra satellites in cloud-free conditions. We found remarkable seasonal and spatial trends in the T-a vs. T-s relationship: (i) T-s are strongly correlated with T-a (R-2 = 0.77, root mean square difference (RMSD) = 5.9 degrees C, n = 11,101 at daily scale and R-2 = 0.80, RMSD = 5.7 degrees C, n = 3552 at 8-day scale); (ii) in general, the RMSD is lower for the winter months in comparison to summer months for all the stations, (iii) the RMSD is directly proportional to the elevations; (iv) the RMSD is inversely proportional to the annual precipitation. Our results demonstrate the statistically strong and previously unreported T-a vs. T-s relationship and spatial and seasonal variations in its intensity at daily resolution for the Western Himalaya. We anticipate that our results will provide the scientists in Himalaya or similar data-deficient extreme environments with an option to use freely available remotely observed T-s products in their models to fill-up the spatiotemporal data gaps related to in situ monitoring at daily resolution. Substituting T-a by T-s as input in various geophysical models can even improve the model accuracy as using spatially continuous satellite derived T-s in place of discrete in situ T-a extrapolated to different elevations using a constant lapse rate can provide more realistic estimates.
Acceso Abierto
Small lava caves as possible exploratory targets on Mars: Analogies drawn from UAV imaging of an Icelandic lava field
(Multidisciplinary Digital Publishing Institute, 2020-06-19) Sam, Lydia; Bhardwaj, Anshuman; Singh, Shaktiman; Martín Torres, Javier; Zorzano, María-Paz; Ramírez Luque, Juan Antonio; 0000-0003-3181-2960; 0000-0002-2502-6384; 0000-0003-4304-388; 0000-0002-4492-9650; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Volcanic-aeolian interactions and processes have played a vital role in landscape evolution on Mars. Martian lava fields and associated caves have extensive geomorphological, astrobiological, and in-situ resource utilization (ISRU) implications for future Mars missions which might be focused on subsurface exploration. Although several possible cave “skylights” of tens to >100 m diameter have been spotted in lava fields of Mars, there is a possibility of prevalence of meter-scale features which are an order of magnitude smaller and difficult to identify but could have vital significance from the scientific and future exploration perspectives. The Icelandic volcanic-aeolian environment and fissure volcanoes can serve as analogs to study lava flow-related small caves such as surface tubes, inflationary caves, liftup caves, and conduits. In the present work, we have tried to explore the usability of unmanned aerial vehicle (UAV)-derived images for characterizing a solidified lava flow and designing a sequential methodology to identify small caves in the lava flow. In the mapped area of ~0.33 km2, we were able to identify 81 small cave openings, five lava flow morphologies, and five small cave types using 2 cm/pixel high-resolution images. The results display the usefulness of UAV imaging for such analogous research, and also highlight the possibility of the widespread presence of similar small cave openings in Martian lava fields. Such small openings can facilitate optimal air circulation within the caves while sheltering the insides from physical weathering and harmful radiations. Using the available best resolution remote sensing images, we extend the analogy through the contextual and geomorphological analysis of several possible pit craters in the Tharsis region of Mars, in a region of extremely vesicular and fragile lava crust with pahoehoe-type morphology. We report two possible pit craters in this region, with diameters as small as ~20 m. The possibility that such small cave openings can lead to vast subterranean hollow spaces on Mars cannot be ruled out considering its low gravity.