Large elements of North India, together with Bihar, Uttar Pradesh, Uttarakhand, Haryana, Delhi, and Punjab, have been grappling with heavy fog since December 2023, together with in the final week.
At round 2 pm on January 16, for instance, the India Meteorological Department (IMD) warned of a excessive chance of “very dense fog” in Haryana, Chandigarh, and Delhi, the place it mentioned visibility could be decrease than 50 metres in “night/morning hours”. It issued comparable alerts for Uttar Pradesh, Punjab, and Madhya Pradesh, the place it mentioned visibility could possibly be restricted to 50-200 metres.
On the social media platform X (Twitter), IMD has additionally accompanied alerts with maps from the INSAT 3D satellite tv for pc, and typically from the INSAT 3DR satellite tv for pc. The fog in these maps is each clearly seen and annotated by IMD. However, what do the maps’ colors imply? And how did the satellites receive these photos from area?
| Photo Credit:
IMD/X (Twitter)
Solar reflectance and brightness temperature
At the backside proper of one in every of the maps was a clue: “Night Microphysics”. According to a paper revealed by IMD scientists in February 2019, the INSAT 3D satellite tv for pc has a red-green-blue, or RGB, imager whose photos’ colors are decided by two components: photo voltaic reflectance and brightness temperature.
Solar reflectance is a ratio of the quantity of photo voltaic power mirrored by a floor and the quantity of photo voltaic power incident on it. Brightness temperature has to do with the relationship between the temperature of an object and the corresponding brightness of its floor. It is completely different from temperature as we often perceive it – like the temperature we ‘feel’ after we contact a glass of sizzling tea – as a result of brightness temperature additionally has to do with how the tea glass emits the thermal radiation, which is at completely different frequencies in several instructions.
INSAT 3D’s ‘day microphysics’ knowledge part research photo voltaic reflectance at three wavelengths: 0.5 µm (seen radiation), 1.6 µm (shortwave infrared radiation) and 10.8 µm (thermal infrared radiation). That is, detectors onboard the satellite tv for pc track radiation coming from over India in these wavelengths.
The power of the 0.5-µm seen sign determines the quantity of inexperienced color; the power of the 1.6-µm shortwave infrared sign, the quantity of purple color; and the power of the 10.8-µm thermal infrared sign, the quantity of blue color. This manner, the INSAT 3D pc determines the color on every level of the picture.
| Photo Credit:
J. Earth Syst. Sci. (2019) 128:36
Day and night time microphysics
According to the paper, “The major applications of this colour scheme are an analysis of different cloud types, initial stages of convection, maturing stages of a thunderstorm, identification of snow area, and the detection of fires.”
How does the satellite tv for pc track snow? While the photo voltaic reflectance of snow and that of clouds is analogous in the seen a part of the spectrum, snow strongly absorbs radiation of wavelength 1.6 µm, i.e. shortwave infrared. As a consequence, when the satellite tv for pc tracks snow, the purple part of the color scheme turns into very weak.
The satellite tv for pc’s ‘night microphysics’ part is a bit more concerned. Here, two colors are decided not by a single sign however by the power of the distinction between two alerts. The pc determines the quantity of purple color in accordance to the distinction between two thermal infrared alerts: 12 µm and 10 µm. The quantity of inexperienced color varies in accordance to the distinction between a thermal infrared and a center infrared sign: 10.8 µm and three.9 µm. The quantity of blue color shouldn’t be a distinction however is decided by the power of a thermal infrared sign of wavelength 10.8 µm.
| Photo Credit:
J. Earth Syst. Sci. (2019) 128:36
For instance, in the picture above, the knowledge signifies three sorts of clouds. (‘K’ denotes the temperature variations in kelvin.) A mature cumulonimbus (“CB”) cell, probably a part of a tropical storm, hangs over West Bengal and is seen principally in purple, however whose blue part signifies it’s also very chilly. Further north of Delhi, flecks of inexperienced dominate, indicating a preponderance of decrease clouds. The sky even additional north is dominated by a excessive and heavy cloud system that encompasses decrease clouds as nicely.
Revealing the ambiance
By combining day and night time microphysics knowledge, atmospheric scientists can elucidate the presence of moisture droplets of various shapes and temperature variations over time, and in flip track the formation, evolution and depletion of cyclones and different weather occasions.
For instance, profiting from the undeniable fact that INSAT 3D can produce photos primarily based on alerts of a number of wavelengths, the authors of the 2019 paper have proposed day and night time microphysics knowledge that they are saying would point out a thunderstorm impending in a single to three hours.
Both INSAT 3D and INSAT 3DR use radiometers to make their spectral measurements. A radiometer is a tool that measures numerous helpful properties of radiation, sometimes by profiting from radiation’s interplay with matter, for instance in the type of temperature or electrical exercise). Both satellites additionally carry atmospheric sounders. These are units that measure temperature and humidity, and research water vapour as a perform of their heights from the floor.
Scientists mix the radiometer and sounder measurements to perceive numerous atmospheric traits.
Another INSAT in 2024
According to the INSAT 3DR brochure, its radiometer is an upgraded model of the very-high-resolution radiometer (VHRR) that the Kalpana 1 and INSAT 3A satellites used (launched in 2002 and 2003, respectively).
The Space Application Centre’s transient for INSAT 3A states: “For meteorological observation, INSAT-3A carries a three channel Very High Resolution Radiometer (VHRR) with 2 km resolution in the visible band and 8 km resolution in thermal infrared and water vapour bands.” The radiometers onboard 3D and 3DR have “significant improvements in spatial resolution, number of spectral channels and functionality”.
The Kalpana 1 and INSATs 3A, 3D, and 3DR satellites aided India’s weather monitoring and warning providers with the greatest know-how out there in the nation at the time, and with every new satellite tv for pc being a better-equipped model of the earlier one. So whereas Kalpana 1 had a launch mass of 1,060 kg and carried a early VHRR and a data-relay transponder, INSAT 3DR had a launch mass of two,211 kg – in 2016 – and carried an upgraded VHRR, a sounder, a data-relay transponder and a search-and-rescue transponder.
India deactivated Kalpana 1 in September 2017, after 15 years in orbit. The INSAT 3D and 3DR satellites are presently energetic in geostationary orbits round the earth, at inclinations of 82 levels and 74 levels east longitudes respectively.
In February 2024, the Indian Space Research Organisation is predicted to launch the INSAT 3DS meteorological satellite tv for pc onboard its GSLV Mk II launch car, with a launch mass of two tonnes. While “3DR” stood for “3D repeat”, “3DS” stands for “3D second repeat”.
This article was first revealed on the creator’s weblog and is republished right here with updates.
- Large elements of North India, together with Bihar, Uttar Pradesh, Uttarakhand, Haryana, Delhi, and Punjab, have been grappling with heavy fog since December 2023, together with in the final week.
- On the social media platform X (Twitter), IMD has additionally accompanied alerts with maps from the INSAT 3D satellite tv for pc, and typically from the INSAT 3DR satellite tv for pc. The fog in these maps is each clearly seen and annotated by IMD.
- At the backside proper of one in every of the maps was a clue: “Night Microphysics”. According to a paper revealed by IMD scientists in February 2019, the INSAT 3D satellite tv for pc has a red-green-blue, or RGB, imager whose photos’ colors are decided by two components: photo voltaic reflectance and brightness temperature.
