The complex housing the S-Band Doppler Weather Radar at the Meteorological Centre in Begumpet, Hyderabad.
| Photo Credit: File Photo
The story so far: After devastating floods and landslides killed more than 200 people in Kerala’s Wayanad district in July 2024, the Union Ministry of Earth Sciences approved an X-band radar to be installed in the district. A torrential downpour triggered the landslide in the valley above Punchirimattom, near the Mundakkai region; its effects were compounded by a massive debris flow triggered by the rains.
How do radars work?
Radar is short for ‘radio detection and ranging’. The device uses radio waves to determine the distance, velocity, and physical characteristics of objects around the device. A transmitter emits a signal aimed at an object whose characteristics are to be ascertained (in meteorology, this could be a cloud). A part of the emitted signal is echoed by the object back to the device, where a receiver tracks and analyses it.
Weather radar, also known as a Doppler radar, is a common application of this device. The Doppler effect is the change in frequency of sound waves as their source moves towards and away from a listener. In meteorology, Doppler radars can reveal how fast a cloud is moving and in which direction based on how the cloud’s relative motion changes the frequency of the radiation striking it.
A pulse-Doppler radar can measure the intensity of, say, rainfall by emitting radiation in pulses and tracking how often they’re reflected to the receiver.
This way, modern Doppler radars can monitor weather conditions and anticipate new wind patterns, the formation of storms, etc.
What is an X-band radar?
Doppler radar relies on Rayleigh scattering, when the scatterer is much smaller than the wavelength of the radiation. A radar trying to ‘see’ smaller particles like rain droplets or fog will need to use radiation of lower wavelengths, like in the X-band. An X-band radar is radar that emits radiation in the X-band of the electromagnetic spectrum: 8-12 GHz, corresponding to wavelengths of around 2-4 cm (this is in the microwave part of the spectrum.)
The smaller wavelengths allow the radar to produce images of higher resolution. However, the greater the frequency of some radiation, the faster it will be attenuated. So X-band radars have a relatively shorter range.
In Wayanad, the new radar is expected to be able to monitor the movements of particles, such as soil, to inform landslide warnings. The device will also perform high temporal sampling, that is, rapidly sample its environs, allowing it to spot particle movements happening in shorter spans of time.
How many radars does India have?
The India Meteorological Department (IMD) started using radar for weather applications in the early 1950s. The first indigenously designed and manufactured X-band storm detection radar was installed in 1970 in New Delhi. In 1996, IMD replaced 10 outdated X-band radars with digital X-band radars.
In its X-band radar network, India has both wind-finding and storm-detecting radars, and some with dual capabilities. The country also uses S-band radars (2-4 GHz) for long-range detection. The first S-band cyclone detection radar was installed in Visakhapatnam in 1970 and the first locally made variant was commissioned in Mumbai in 1980.
In September 2024, the Ministry of Earth Sciences said India is set to have 56 additional Doppler radars in a few years. On September 11, the Union Cabinet cleared the ₹2,000-crore ‘Mission Mausam’ to upgrade meteorological infrastructure in the country. This includes installing up to 60 meteorological radars until 2026 under the Mission’s first phase.
Minister of State for Earth Sciences Jitendra Pradhan said in August in Parliament that the government has started the process to procure and install 10 X-band Doppler radars to improve weather forecasting in the northeast States and in Himachal Pradesh’s Lahaul and Spiti district.
The initiative to install an X-band radar in Wayanad included installing a C-band radar (4-8 GHz) with an observational range of 250 km in Mangaluru.
What is NISAR?
NASA and the Indian Space Research Organisation (ISRO) are currently developing a satellite called NISAR, short for ‘NASA-ISRO Synthetic Aperture Radar’. It will use radar imaging to produce a high-resolution map of the earth’s landmasses.
Its payload consists of an L-band radar (1.25 GHz, 24 cm) built by NASA and an S-band radar (3.2 GHz, 9.3 cm) built by ISRO. Together they will track and record changes in the earth’s various natural processes.
It is currently expected to be launched onboard an ISRO GSLV Mk II rocket in 2025, at a total cost of $1.5 billion, the bulk of it borne by NASA.
Published – October 14, 2024 08:30 am IST