GEOG 380 - Lab 08

Remote sensing

What is multispectral imagery?

Imagery collected in multiple wavelength bands of the electromagnetic spectrum, not just visible light.

What is a spectral band?

A specific range of wavelengths recorded by a sensor as one image layer.

What is the main advantage of multispectral imagery?

Different surfaces reflect energy differently in different bands, helping identify land-cover types and environmental conditions.

What satellite sensor was used in this lab?

Sentinel-2 MSI.

What is a single-band image?

A grayscale image showing pixel values for only one spectral band.

What does DN stand for?

Digital Number.

What is a digital number (DN)?

The numerical pixel value representing the recorded signal intensity in a band.

Why compare the same feature in two different bands?

Because features may appear brighter or darker in different wavelengths, which helps identify them.

Why is water often dark in near-infrared imagery?

Because water absorbs much of the near-infrared energy.

Why is healthy vegetation bright in near-infrared imagery?

Because leaf structure strongly reflects near-infrared radiation.

Why are clouds often bright in many bands?

Because they reflect a lot of incoming radiation.

What is image contrast?

The visual difference in brightness or colour between features.

Why is stretching used in image display?

To improve visibility of differences between features by redistributing display values.

What does Percent Clip stretch do?

It clips a small percentage of extreme high and low values to improve overall image contrast.

What is a multiband image?

A raster that stores several spectral bands in one dataset.

Why create a multiband image?

To make colour composites, compare bands more easily, and calculate indices like NDVI.

Why does band order matter when compositing bands?

Because bands are renamed by input order, and wrong ordering can make later interpretation confusing.

What does RGB stand for?

Red, Green, Blue.

What is an RGB composite?

An image made by assigning selected spectral bands to the red, green, and blue display channels.

Why do remote sensing colours not always match real-world colours?

Because spectral bands are often assigned to display channels artificially for interpretation purposes.

What is a natural colour composite?

A composite where visible red, green, and blue bands are assigned to matching RGB channels.

Why can natural colour images have low contrast?

Because many land-cover types have similar reflectance in visible wavelengths.

What is a CIR composite?

A Colour Infrared composite that assigns near-infrared to red, red to green, and green to blue.

Why does vegetation appear red in a CIR image?

Because vegetation strongly reflects near-infrared, and NIR is displayed in the red channel.

Why is CIR often more contrasty than natural colour?

Because near-infrared better separates vegetation from other surfaces.

What is a false colour composite?

A composite that uses a non-natural assignment of spectral bands to RGB channels.

Why use a false colour composite?

To highlight features such as vegetation, moisture differences, and land-cover variation more clearly.

Does “false colour” mean the image is incorrect?

No. It means the displayed colours are intentionally assigned and not natural eye colours.

What happens if the same band is assigned to red, green, and blue?

The image appears grayscale because all three channels have the same value.

Why compare natural colour and false colour images?

To see how feature appearance changes depending on the spectral bands used.

What is a spectral index?

mathematical combination of bands designed to highlight a particular surface property.

What does NDVI stand for?

Normalized Difference Vegetation Index.

What is the NDVI formula?

(NIR−Red)/(NIR+Red).

Why does NDVI work for vegetation?

Because healthy vegetation reflects strongly in NIR and absorbs red light.

What do high NDVI values usually indicate?

Dense or healthy vegetation.

What do NDVI values near zero usually indicate?

Bare soil, rock, or built surfaces.

What do negative NDVI values often indicate?

Water or other non-vegetated surfaces.

Why can cropland have variable NDVI values?

Because crop type, growth stage, irrigation, soil exposure, and plant health can vary.

Why might mountain areas have lower NDVI than agricultural land?

Because they often have less dense vegetation, more rock, and different land cover.

Why classify NDVI into classes?

To make vegetation patterns easier to interpret on the map.

What is the purpose of symbology in image analysis?

To make patterns and differences easier to see and interpret.

What are the two main outputs required in this lab?

A false colour map and an NDVI map.

Why is map layout important?

Because a map must clearly communicate what the data shows and how to interpret it.

What should explanatory text on a map do?

Explain what the map shows and how the colours or values should be interpreted.

What is one big lesson from this lab?

Satellite imagery interpretation depends on understanding spectral reflectance, band combinations, and how image values relate to real-world features.