Site Quality Analysis for an Indian Submillimeter Telescope: A Reanalysis-Based Approach
Tanmay Singh, Mayuri Sathyanarayana Rao, Ritoban Basu Thakur
TLDR
This paper reanalyzes ERA5 data to identify optimal submillimeter telescope sites in Ladakh, India, finding two promising locations with low precipitable water vapor.
Key contributions
- Analyzed 15 years of ERA5 reanalysis data for precipitable water vapor (PWV) across Ladakh, India.
- Identified two promising submillimeter telescope sites (A & B) in Ladakh with PWV ≤ 1 mm for 19-23% of the time.
- Computed atmospheric transmittance and photon noise for candidate sites, comparing performance to global observatories.
- Found Sites A and B significantly outperform existing Hanle and Merak locations for submillimeter observations.
Why it matters
This research provides crucial data for selecting a prime location for India's next-generation submillimeter observatory in Ladakh. By leveraging reanalysis data, it efficiently identifies highly suitable sites, reducing initial exploration costs and accelerating the development of new astronomical capabilities. The findings highlight Ladakh's potential as a world-class submillimeter astronomy hub.
Original Abstract
The Himalayan plateau region of Ladakh, India, is a potential host for a science-class submillimeter observatory, building on existing astronomical infrastructure near Hanle and Merak. Using the fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA5) data, we analyze precipitable water vapor (PWV) at monthly resolution over 184 months from January 2010 to April 2025, map PWV statistics across Ladakh, and identify candidate regions that reach PWV $\leq 1$ mm. For promising locations, we compute atmospheric transmittance and the corresponding atmospheric photon noise using the am (Atmospheric Model) radiative transfer code; we present transmittance and brightness temperature estimates over 10--1000 GHz and compare the inferred performance to sites hosting current or planned submillimeter facilities worldwide. We find Ladakh to be favorable for submillimeter observations, with multiple ERA5 grid cells reaching PWV $\leq 1$ mm. Within ERA5's spatial resolution, two regions emerge as particularly promising: Site A ($\approx 34.25^\circ$N, $78.75^\circ$E) and Site B ($\approx 32.50^\circ$N, $79.00^\circ$E), which satisfy PWV $\leq 1$ mm for about 23% and 19% of the study duration, respectively, compared to about 5% and 8% for the Hanle and Merak grid cells. These results motivate targeted in situ radiometer measurements for final site selection.
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