To start with, let me explain about, What is a RADAR? It is an object detection system that uses radio waves to determine the range, altitude, direction, and speed of objects. Its been used to detect aircraft, ships, spacecrafts, guided missiles, weather formations, and terrain. Now that you know about what a RADAR does, let me give you some information about a RADAR which has done something interesting recently to provide us with more research opportunities to study about probing planetary bodies at National Atmospheric Research Laboratory (NARL).

An MST (Mesosphere-Stratosphere-Troposphere) RADAR which has high power and large aperture established at NARL, Gadanki was designed to study the middle and upper atmosphere dynamics, but this was not actually meant to study the moon.

It (MST Radar) is now recently upgraded by ISRO Scientists to detect echoes from the moon. Detection of moon echoes enables us an opportunity to characterise the large phased array antenna system including the calibration of the radar.

It is given that the Radio Frequency pulse has to travel for approximately 2.5 seconds to return to the RADAR from the moon’s surface. Since the RADAR was not meant to study the moon in the first place, the experiment was conducted cleverly in range-ambiguous mode in such a way that the range folded echoes form the moon fall in the height region where apparent source of atmospheric echoes were absent.

The RADAR beam was positioned accordingly so as to receive the moon echoes while it was apparently transiting from East to West.

Results:

The experiment was successful and the results obtained are:

  • The results which are obtained now are consistent with those acquired earlier at similar frequencies.
  • The moon echoes are found to have SNR (Signal-to-Noise Ratio) as high as 20 dB.
  • Echo power changes as the radar pulse travels from the sub-terrestrial point towards the limbs consistent with the angular dependence of echo power.
  • Doppler spectral property changes from narrow single peak spectrum to multi-peak spectrum as the radar pulse travels from the sub-terrestrial point towards the limbs.
  • Multi-peak spectra are found to be originating from multiple discrete targets on the moon.

RADAR techniques are being used by ISRO Scientists since decades for studying the moon ever since the radio signals reflected from the moon were detected using ground based radar.

Since then, both ground-based and satellite-based RADARs are employed to study the moon’s topography, impact craters morphology, and Goliath.

Future missions:

  • Scientists are planning to employ the delay-Doppler technique on the MST RADAR for mapping the moon’s surface.
  • To upgrade MST RADAR for incoherent scatter RADAR applications.
  • Then obtained observations would be compared with Chandrayaan-1 to understand the Moon’s surface.
  • To study Very High Frequency echoes from the moon.
  • To study ionospheric effects on radio experiments.
narl_mst_radar_observes_echoes_from_the_moon

In this figure, the true range = observed range + 3,67,740 km. SNR of moon echoes as a function of ambiguous-range and time observed in different beams. Echoes marked as A, B, C, D and E correspond to observations made in 18* East, 12* East, 6* East, Zenith, and 6* West beams respectively.

Details on echo characteristics and its implications can be found in a research paper published recently in Current Science: Click here

Link to MST Radar: Click here

Information acquired from: isro.gov.in