BENGALURU: While scientists have been using satellite images of the Earth at night — Night Time Light (NTL) — to study human activity and natural events for over three decades, economists, too, have followed suit in recent years, realising how this can help gauge a variety of indicators.
“In fact, if aliens were ever to approach Earth from its dark side, they would already know some basics about the global economy,” an IMF publication on ‘how satellite images at night reveal the pace of economic growth and much more’ reads.
In this context, the NTL Atlas — Decadal Change of NTL over India from Space (2012-2021), released by Isro’s National Remote Sensing Centre (NRSC) — shows that overall at the national level, normalised NTL radiance increased by 43% in 2021 compared to 2012.
NRSC used data from NASA and NOAA (National Oceanic and Atmospheric Administration) for the analysis and NTL data provided is the cumulative radiance divided by the total geographical area. That is, nationally it is for the geographical area of the entire country and for states and districts, it’s those respective administrative boundaries.
A state-wise analysis shows that in developed states like Maharashtra, Karnataka, Tamil Nadu, Andhra-Telangana, percentage increase is moderate — all under 55% — because of a higher base number in 2012, while lesser-developed states have recorded a greater growth in percentage terms.
According to NRSC, NTL annual composite is chosen for decadal time series analysis to analyse national, state and district-wise NTL trends. The datasets are processed for geotag, mosaic, extract as per administrative boundaries and calculate statistics to perform trend analysis. Annual normalised Sum of Lights (SoL) is calculated by aggregating the total radiance divided by total geographic area at different administrative units.
“Significant increase was observed in Bihar (474%), Manipur (441%), Ladakh (280%) and Kerala (119%), while good increase was observed in Arunachal Pradesh (66%), Madhya Pradesh (66%), Uttar Pradesh (61%) and Gujarat (58%),” the Atlas read.
According to the Atlas, moderate increase was observed in Lakshadweep, Maharashtra, Tamil Nadu, Jharkhand, Haryana, Punjab, West Bengal, Uttaranchal, Karnataka, Odisha, Telangana, Andhra Pradesh, Nagaland, Chandigarh, Himachal Pradesh, Rajasthan, Tripura, Goa, Chhattisgarh, Assam, Andaman & Nicobar, Meghalaya and Jammu & Kashmir.
While the increase in six states/UTs has been classified insignificant, in 21 states/UTs the increase is in the range of 6% and 40% (see graphic). “NTL represents the intensity of artificial lights which can be related to many dimensions of development.
NTL data is obtained from sensors onboard combined missions of Nasa and NOAA… These products can be used for spatio-temporal trend analysis to understand its relationship with environmental changes and socio-economic parameters like electricity consumption, GDP, population, urban expansion, poverty etc,” said Prakash Chauhan, director, NRSC.
Globally, it’s not just the IMF, the World Bank, Asian Development Bank (ADB) and other institutions and organisations have been increasingly looking at night images of satellites to decipher various socio-economic indicators.
The ADB, in one of its blogs, for instance, says NTLs are much more than decoration — they provide data that can help determine socio-economic indicators when no other reliable information exists, while a similar observation is also made by the World Bank.