Introduction

As large parts of North India, including regions like Bihar, Uttar Pradesh, Uttarakhand, Haryana, Delhi, and Punjab, grapple with heavy fog, the India Meteorological Department (IMD) has been issuing alerts and warnings to keep residents informed about the prevailing conditions.
This article seeks to unravel the science behind these warnings and the role of the INSAT 3D satellite in providing crucial data for fog monitoring.

Fog Situation in North India

Persistent Fog: Since December 2023, many parts of North India have been shrouded in heavy fog.
IMD Warnings: On January 16, the IMD issued warnings about “very dense fog” in several states, including Haryana, Chandigarh, Delhi, Uttar Pradesh, Punjab, and Madhya Pradesh, with visibility expected to drop below 50 meters during night and morning hours.

Insights from INSAT 3D: The INSAT 3D satellite plays a vital role in monitoring foggy conditions through images.
Solar Reflectance and Brightness Temperature: The colors in these images are determined by two factors: solar reflectance and brightness temperature.
Solar Reflectance: Reflects the amount of solar energy reflected by a surface in relation to the energy it receives.
Brightness Temperature: Relates an object’s temperature to the brightness of its surface, measured across various wavelengths.

Solar Reflectance at Three Wavelengths: INSAT 3D’s ‘day microphysics’ component studies solar reflectance at three wavelengths: 0.5 µm (visible radiation), 1.6 µm (shortwave infrared radiation), and 10.8 µm (thermal infrared radiation).
Color Determination: The strength of signals at these wavelengths determines the RGB (red-green-blue) colors in the image.
Applications: These images help analyze cloud types, thunderstorm stages, snow identification, and fire detection.

Complex Color Determination: INSAT 3D’s ‘night microphysics’ component derives two colors from the difference between two thermal infrared signals.
Color Variables: Red color depends on the difference between 12 µm and 10 µm signals, green on 10.8 µm and 3.9 µm signals, and blue on the strength of the 10.8 µm signal.
Identifying Features: Night microphysics data aids in identifying cloud types and their temperature differences.

Comprehensive Insights: Meteorologists combine day and night microphysics data to study moisture droplets, temperature variations, and track the formation, evolution, and depletion of weather events, including cyclones.
Advanced Warning Systems: Proposed applications include predicting thunderstorms one to three hours in advance.

Satellite Instruments: INSAT 3D and 3DR use radiometers for spectral measurements and atmospheric sounders for temperature, humidity, and water vapor analysis.
Improved Technology: These satellites offer significant improvements in spatial resolution and spectral channels compared to their predecessors, enhancing India’s weather monitoring capabilities.

Continued Advancements: The Indian Space Research Organisation plans to launch the INSAT 3DS meteorological satellite in February 2024.
Enhanced Capabilities: This satellite will build upon the successes of its predecessors, further enhancing India’s weather monitoring and warning capabilities.

The INSAT 3D satellite, with its ability to capture and analyze day and night microphysics data, plays a pivotal role in monitoring and predicting weather conditions, including foggy scenarios, in North India.
By understanding the intricate science behind these satellite images, meteorologists can provide timely warnings and valuable insights to protect public safety and navigate the challenges posed by severe weather conditions.
With advancements on the horizon, India’s meteorological capabilities continue to evolve, ensuring better preparedness for weather-related events in the future.