Large parts of North India, including Bihar, Uttar Pradesh, Uttarakhand, Haryana, Delhi, and Punjab, have been grappling with heavy fog since December 2023, including in the last week.
At around 2 pm on January 16, for example, the India Meteorological Department (IMD) warned of a high likelihood of “very dense fog” in Haryana, Chandigarh, and Delhi, where it said visibility would be lower than 50 metres in “night/morning hours”. It issued similar alerts for Uttar Pradesh, Punjab, and Madhya Pradesh, where it said visibility could be limited to 50-200 metres.
On the social media platform X (Twitter), IMD has also accompanied alerts with maps from the INSAT 3D satellite, and sometimes from the INSAT 3DR satellite. The fog in these maps is both clearly visible and annotated by IMD. However, what do the maps’ colours mean? And how did the satellites obtain these images from space?
