Sensors and Imagery 2

What are atmospheric windows?

Wavelength ranges where gases like water vapor, CO₂, and ozone absorb very little radiation, allowing specific wavelengths to pass through almost freely.

Why are atmospheric windows important?

They determine which parts of the electromagnetic spectrum can be effectively used for remote sensing.

What is radiant flux (Φ)?

The time rate of flow of energy onto, off of, or through a surface; measured in watts (W).

What is irradiance?

Amount of radiant flux incident upon a surface from all directions per unit area (W/m²).

What is exitance?

Amount of radiant flux leaving a surface into all directions per unit area (W/m²).

What is radiance (L)?

Radiant flux per unit solid angle leaving a source in a given direction per unit projected area (W/m²·sr).

What is a steradian (sr)?

Unit of measure for solid angles in 3D space.

What is reflectance?

Dimensionless ratio of radiant flux reflected from a surface to radiant flux incident on it.

Why can't satellites measure exitance directly?

They only measure radiance (L) within their instantaneous field of view (IFOV).

How are remotely sensed images stored?

As raster data, with each band stored as a separate raster layer.

What is a pixel in remote sensing?

A picture element representing a uniform grid cell in a raster image.

What is a digital number (DN)?

A pixel value representing the amount of measured radiance.

What is a raster image?

A uniform grid of pixels, each with a DN corresponding to radiance for a band.

What is a band in raster data?

An image layer representing a specific wavelength (e.g., red, green, NIR).

What are RGB images?

Images that display 3 bands corresponding to red, green, and blue, where colors are additive (R+G+B=white).

Types of resolution in remote sensing

Spatial, Spectral, Radiometric, Temporal.

What is spatial resolution?

The size of the field of view or pixel (e.g., 10 × 10 m).

What is spectral resolution?

Number and width of spectral bands a sensor records (e.g., panchromatic, multispectral, hyperspectral).

What is temporal resolution?

How often a sensor acquires data for the same area (e.g., every 30 days).

What is radiometric resolution?

Sensor sensitivity to small differences in electromagnetic energy (e.g., 1-bit, 8-bit, 16-bit).