At night, Bangladesh glows. Not faintly, not intermittently, but with a brightness that has been intensifying for three decades. DMSP-OLS satellites first recorded the country's nighttime radiance in 1992, measuring a national mean of 1.58 units. By 2012, the last year of the DMSP era, that figure had nearly doubled to 2.87. When the more sensitive VIIRS instrument took over in 2014, it captured an even more granular picture of the transformation: national mean radiance climbed from 0.38 in 2014 to 0.92 in 2024, a 141% increase in a single decade.
Every photon in the nightlight record represents a human decision. A factory turning on. A street lamp installed. A household connected to the grid. But not every photon is progress. Some represent the unplanned sprawl of cities that are expanding faster than any government can regulate. Others mark the industrial zones whose emissions are slowly poisoning the air their workers breathe.
This is the story of Bangladesh's luminous transformation, told through satellites that never sleep.
The lights are on
The nightlight record for Bangladesh spans two satellite eras: DMSP-OLS (1992-2012) and VIIRS-DNB (2014-2024). The two sensors use different radiance scales, so direct comparison of absolute values across the 2013 boundary is misleading. But within each era, the trajectory is unmistakable.
During the DMSP period, national mean radiance rose from 1.58 in 1992 to a peak of 2.98 in 2010, before settling at 2.87 in 2012. The dip in 2006 (1.58, identical to the 1992 baseline) is likely an artifact of sensor calibration rather than an actual regression, since surrounding years show steady growth. Total sum radiance tells the same story: from 242,282 in 1992 to 440,775 in 2012, an 82% increase.
The VIIRS era, with its finer resolution and wider dynamic range, reveals the acceleration continuing. Mean radiance rose from 0.38 in 2014 to 0.92 in 2024. Sum radiance more than doubled, from 58,755 to 141,462. The most dramatic jump occurred between 2016 and 2018, when mean radiance leapt from 0.38 to 0.64, coinciding with Bangladesh's push toward universal electrification.
The city-level data from 2024 reveals where the light is concentrated. Narayanganj, the industrial twin of Dhaka, leads the country with a mean radiance of 8.81, followed by Dhaka at 7.37 and Chittagong at 6.75. These three cities alone produce more light per unit area than the next seven cities combined. Gazipur (4.10) and Comilla (3.39) form a second tier. The remaining five cities, including divisional capitals like Rangpur (2.09) and Barishal (2.52), cluster between 2 and 3.1 units of radiance.
This concentration is itself a policy signal. When three urban cores generate most of a country's nighttime light, it means economic activity is dangerously concentrated. If Dhaka-Narayanganj-Chittagong were disrupted by a flood, cyclone, or pandemic lockdown, the economic impact would be visible from space as a sudden dimming.
The concrete is spreading
The nightlights tell you where activity is happening. The built-up area data tells you where the earth has been permanently transformed. The Global Human Settlement Layer, derived from Landsat imagery at 30-meter resolution, provides this record from 1975 to 2020.
In 1975, Bangladesh had approximately 456 km2 of built-up land. By 1990, that had nearly tripled to 1,322 km2. By 2000, it reached 1,711 km2. And by 2020, the national built-up footprint stood at 2,678 km2.
That is a 488% increase in 45 years. Nearly 2,222 km2 of land that was once paddy field, wetland, or forest is now concrete, brick, and asphalt. To put that in context, the entire Dhaka metropolitan area occupies roughly 300 km2, meaning Bangladesh has paved over an area equivalent to seven Dhakas since 1975.
The rate of expansion is not slowing. Between 1975 and 1985, Bangladesh added 482 km2 of built-up area (48.2 km2/year). Between 2010 and 2020, it added 535 km2 (53.5 km2/year). The pace has remained remarkably consistent at around 50 km2 per year for the past four decades, but the denominator, the remaining unconverted land, is shrinking. Each new square kilometer of concrete now displaces a higher proportion of what is left.
The fastest expansion has occurred along transport corridors: the Dhaka-Chittagong highway, the Dhaka-Mymensingh corridor, and the ribbon development that has turned Gazipur from a semi-rural district into an extension of Dhaka's urban fabric. These are not planned cities expanding according to master plans. They are accretions: factories, housing colonies, and commercial strips that grow organically along roads and rivers, with drainage and sewage infrastructure added (if ever) as an afterthought.
The air is poisoned
The price of urbanization is measured not only in lost farmland but in degraded air. Sentinel-5P, launched in 2017, provides the first consistent satellite record of tropospheric nitrogen dioxide (NO2) over Bangladeshi cities. The 2023 data reveals a geography of pollution that mirrors the nightlight and built-up area maps almost exactly.
Narayanganj records the highest mean NO2 concentration at 200.99 umol/m2, followed by Gazipur at 180.53 umol/m2 and Dhaka at 170.08 umol/m2. These three cities form the industrial heart of Bangladesh, and they share the same air mass. A factory in Gazipur does not pollute only Gazipur; its emissions drift south across Dhaka and Narayanganj in a continuous plume.
The gap between the top three and the rest is vast. Chittagong, the second-largest city, registers only 69.12 umol/m2, less than half of Dhaka's level. Rajshahi (57.85 umol/m2) and Comilla (52.80 umol/m2) occupy the middle tier. The cleanest cities in the dataset, Sylhet (37.79 umol/m2) and Rangpur (38.87 umol/m2), breathe air with roughly one-fifth the NO2 concentration of Narayanganj.
NO2 is both a direct health hazard (respiratory inflammation, increased asthma risk, cardiovascular damage) and a precursor to ground-level ozone and fine particulate matter. The satellite cannot measure PM2.5 directly, but the NO2 map is a reliable proxy for the broader air quality crisis. Where NO2 is high, PM2.5 is almost certainly high as well.
The urban heat island effect compounds the air quality problem. Satellite-derived land surface temperature data shows that cities are significantly hotter than their rural surroundings.
Dhaka registers an urban land surface temperature of 30.91 degrees Celsius, compared to 28.86 degrees in surrounding rural areas: a UHI intensity of 2.05 degrees. Chittagong shows a similar pattern, at 1.93 degrees above rural baseline. Khulna runs 1.70 degrees hotter. Only Rajshahi (0.57 degrees) shows a relatively modest urban heat premium, likely because its surrounding landscape is already warm and dry.
Higher urban temperatures accelerate the photochemical reactions that convert NO2 into ozone. They increase energy demand for cooling, which in turn increases power plant emissions. And they directly harm human health: heat stress, dehydration, and heat stroke disproportionately affect outdoor workers and the urban poor who lack air conditioning. The UHI effect and air pollution are not separate problems. They are the same problem, driven by the same cause: unplanned, concrete-heavy urbanization without adequate green space, ventilation corridors, or emissions controls.
What the satellites cannot see
The nightlight record cannot distinguish between a well-lit street and a diesel generator running illegally behind a garment factory. The built-up area classification cannot tell you whether a building has running water, structural integrity, or fire exits. The NO2 map cannot count the children with asthma in Gazipur or the construction workers breathing brick kiln dust in Narayanganj.
Satellites measure surfaces, not suffering. They detect radiance, not inequality. The fact that Narayanganj glows brightest in the nightlight record and also leads the country in NO2 pollution is not a coincidence. It is a compression of economic desperation into a single geography: the workers who need the factory jobs, the factory owners who resist emission controls, and the municipal authorities who lack the budget or mandate to enforce them.
The satellite data also cannot capture the informal economy that operates in the gaps. The roadside welders, the recycling yards, the leather tanneries that relocated from Hazaribagh to Savar but brought their pollution with them. These are below the spatial resolution of any orbiting sensor, but their cumulative impact is not.
What policy must do
The satellite evidence points to three interventions.
First, deconcentrate economic activity. The fact that three contiguous cities (Dhaka, Gazipur, Narayanganj) produce the most light, the most built-up area, and the most NO2 is evidence of a spatial planning failure. Bangladesh has designated economic zones in Rajshahi, Khulna, and Rangpur, but the nightlight data shows they are not yet generating enough activity to register as significant brightening. Tax incentives, infrastructure investment, and regulatory streamlining in secondary cities must be scaled up until the nightlight map shows multiple bright clusters, not one.
Second, enforce emission standards in the Dhaka-Gazipur-Narayanganj corridor. At 170-201 umol/m2 of NO2, these cities are running an open-air experiment on what happens when millions of people breathe industrial exhaust continuously. Brick kilns, garment factories, and vehicles are the primary sources. The technology to reduce emissions exists and is deployed in peer countries. What is missing is enforcement. The Department of Environment needs real-time monitoring stations linked to penalty mechanisms, not annual inspections that can be anticipated and gamed.
Third, mandate green infrastructure in all new urban development. The UHI data shows that urban surfaces run 1.7 to 2.1 degrees hotter than surrounding countryside. Every building permit in Bangladesh should require a minimum ratio of permeable surface, tree cover, and ventilation corridors. This is not aesthetic preference. It is a public health necessity. A 2-degree reduction in UHI intensity would reduce peak energy demand, lower heat-related mortality, and slow the photochemical production of ozone.
Bangladesh's glow is a sign of ambition, aspiration, and growth. But it is also a sign of a country that is urbanizing without the infrastructure to sustain its cities, producing wealth without distributing it, and consuming air that is slowly killing its people. The satellites see the glow. They do not see the cost, but the data lets us calculate it.
This is Part 2 of the "Satellite Bangladesh" series. Part 3 will examine what is happening to the land: forest loss, vegetation health, and the battle between crops and concrete.
Data Sources
- Nighttime Lights (DMSP-OLS): NOAA National Centers for Environmental Information, Defense Meteorological Satellite Program. 1992-2013. Resolution: ~2.7 km.
- Nighttime Lights (VIIRS DNB): NASA/NOAA Suomi NPP VIIRS Day/Night Band. 2014-2024. Resolution: ~750 m.
- Built-up Area (GHSL): European Commission Joint Research Centre, Global Human Settlement Layer. 1975-2020. Resolution: 30 m (Landsat-derived).
- Tropospheric NO2 (Sentinel-5P TROPOMI): European Space Agency, Copernicus Sentinel-5 Precursor. 2019-2023. Resolution: 3.5 x 7 km.
- Land Surface Temperature (MODIS): NASA Terra/Aqua MODIS LST (MOD11/MYD11). Used for urban heat island analysis. Resolution: 1 km.
- Administrative Boundaries: geoBoundaries ADM2, William & Mary geoLab.