Nadir & viewing geometry

“Nadir” is the point straight down beneath a satellite. “Viewing geometry” describes the angles between the sensor, the ground spot, and the Sun — whether the instrument looks straight down or off to the side.

Why it matters

The same surface looks different depending on the angle it’s viewed and lit from, so knowing the geometry is essential to correct images and compare measurements taken at different times.

Where you’ll meet it

• MODIS and VIIRS scan far to either side of nadir, so their products record view angle for correction.
• MISR deliberately viewed each scene from nine different angles to study clouds and aerosols.
• Landsat points near nadir for consistent, low-distortion imagery.

In plain terms

It’s like looking at a window — straight on it’s clear glass, but at a sharp angle it glares and reflects. Where the Sun and your eye sit changes what you see.