# Polarisation and Brightness Temperature Observations of Venus with the GMRT

## TL;DR

This study used the GMRT to observe Venus at multiple radio frequencies, deriving brightness temperatures and dielectric properties, confirming previous data at higher frequencies and providing new upper limits at lower frequencies.

## Contribution

It presents new brightness temperature measurements of Venus at 1297.67 MHz and 607.67 MHz, and establishes a lower upper limit at 233.67 MHz, along with dielectric constant estimates from polarisation data.

## Key findings

- Brightness temperatures of 622K at 1297.67 MHz and 554K at 607.67 MHz.
- Upper limit of 321K for brightness temperature at 233.67 MHz.
- Dielectric constant of Venus surface estimated to be ~4.5 at key frequencies.

## Abstract

Venus was observed at frequencies of 1297.67 MHz (23 cm), 607.67 MHz (49 cm) and 233.67 MHz (1.28 m) with the Giant Metrewave Radio Telescope (GMRT) during the period of 25th July and 6th September 2015 when it was close to its inferior conjunction. Values of the brightness temperature (Tb) of Venus from these observations were derived as 622{\pm}43 K, 554{\pm}38 K for 1297.67 and 607.67 MHz frequencies, respectively, are in agreement with the previous observations. The attempt to derive the Tb at 233.67 MHz affirms an upper limit of 321 K which is significantly lower than the previously reported upper limit of 426 K at the same frequency. We also present the dielectric constant ({\epsilon}) values of the Venus surface estimated using the degree of polarisation maps of Venus, derived from the GMRT polarisation observations and theoretical calculations. The {\epsilon} of the Venus surface was estimated to be ~4.5 at both the 607.67 MHz and 1297.67 MHz, close to the reported values of {\epsilon} of 4 to 4.5 from the radar-based observations including the Magellan observations at 2.38 GHz (12.6 cm).