Model answer

Landsat is the granddaddy of Earth observation — running continuously since 1972, longer than any other civilian satellite series.

It captures the whole Earth every 16 days (or every 8 days now, with Landsat 8 + 9 working together) at moderate detail (30 m). The data is free, which is why it’s the backbone of every long-term land-change study you’ve heard of: Amazon deforestation, glacier retreat, urban sprawl, agriculture monitoring.

Modern sensors are OLI-2 (visible/NIR/SWIR) and TIRS-2 (thermal infrared).

🔬 Show the science / technical version

• Longest continuous EO record (1972–present, USGS / NASA).
• Orbit 705 km (L4 onward), sun-synchronous, 16-day repeat (L8 + L9 combined ≈ 8-day).
• Modern sensors: OLI-2 (9 bands @ 30 m, pan @ 15 m) + TIRS-2 (2 thermal @ 100 m).
• Heritage TM/ETM+ numbering: 1 Blue, 2 Green, 3 Red, 4 NIR, 5 SWIR-1, 7 SWIR-2, 6 Thermal.
• NDVI: TM B4/B3 → OLI B5/B4 (numbering shifted by 1).