False colour composite

Also called: FCC · Topic: Remote Sensing, GIS and GNSS · NCERT: Class 11, Ch 6 "Introduction to Remote Sensing"

Meaning

A false colour composite (FCC) is one colour picture made by joining three bands, where each band is shown in a colour that does not match its real wavelength. In the standard FCC, green light is shown as blue, red light as green and near-infrared (NIR) as red.

• It matters because the human eye cannot see near-infrared. FCC makes that invisible infrared signal visible, so healthy vegetation shows up clearly in red.
• This makes FCC the basic tool for mapping crops, forests, water and damaged land.

Explanation

How a composite is built

• Band: one narrow part of the electromagnetic spectrum (the full range of light and other energy) that a sensor records separately, for example green, red or near-infrared.
• Display colours: a screen makes every colour by mixing three colours: blue, green and red.
• Composite: three bands are joined into one picture. Each band goes to one display colour.
• Natural colour composite (NCC): each band goes to its own true colour. The picture looks like a normal photograph.
• False colour composite (FCC): the bands are moved to colours that are not their own.

Standard FCC assignment:

Band recorded	Colour shown on screen
Green	Blue
Red	Green
Near-infrared (NIR)	Red

Why healthy vegetation looks red (cause → process → result)

• Cause:
• Chlorophyll (the green colouring in leaves) absorbs red light.

• The inner cell structure of a healthy leaf reflects NIR very strongly.

• Process:

• In standard FCC, the strong NIR signal is shown in red.

• The weak red signal is shown in green, so very little green gets mixed in.

• Result:

• Healthy vegetation appears red.
• Brighter red means denser, healthier plant cover.
• Sick, dry or thin plants reflect less NIR, so they look duller.

Standard FCC colours of land features (NCERT Table 6.2)

Feature	Colour in standard FCC	Simple reason
Evergreen forest	Red to magenta	Dense leaves all year, so very high NIR
Deciduous forest	Brown to red	Leaves fall in one season, so less NIR than evergreen
Cropped land	Bright red	Healthy, actively growing crop
Fallow land	Light blue to white	Bare soil and no plants, so no red
Clear water	Dark blue to black	Water absorbs NIR and most red light
Turbid water	Light blue	Silt floating in the water reflects more green light, which is shown as blue
Dense built-up area	Dark blue to bluish green	Concrete and roofs reflect green and red but little NIR
Sand and salt-affected land	Light blue to white	High reflection in all bands
Waterlogged land	Mottled black	Patches of standing water mixed with wet soil

• Key reading rule: red tones mean plants. Blue and black tones mean water, bare land or buildings.
• Greys and whites in Landsat FCCs show urban or rocky surfaces [5].

Conditions it needs

• A multispectral sensor: a sensor that records several bands at the same time, including a near-infrared band. Without NIR there is no red for vegetation.
• Landsat-1 MSS recorded 4 bands: green, red and two near-infrared [4].

• IRS-1A LISS-I and LISS-II each recorded 4 bands in the visible and near-infrared range [6].

• Digital numbers (DN): each pixel (the smallest cell of a digital image) stores a DN, which is the average brightness of one ground cell. A computer turns the DNs of the three bands into the three display colours.

• A trained interpreter: FCC colours are used together with the other elements of visual interpretation (tone, texture, shape, pattern, association).
• Tone or colour is the first of these elements.

Where it occurs

• India, Bhuvan (ISRO–NRSC geoportal, a website for maps and satellite data):
• Some data is shown as NCC by default. Users can switch to FCC [3].
• Resourcesat LISS-III data (23.5 m) can be downloaded free, with a time lag of 2 years [2].

• LISS-III has 3 visible/near-infrared bands and 1 short-wave infrared band [2].

• India, Indian Remote Sensing (IRS) series:

• IRS-1A was launched on 17 March 1988 from Baikonur into a polar sun-synchronous orbit (an orbit that crosses each place at the same local time every day) [6].

• Its visible and near-infrared bands could be combined into FCCs [6].

• India, examples seen in FCC:

• Turbid water (light blue): silt-laden rivers such as the Ganga and Brahmaputra in flood.
• Salt-affected land (light blue to white): parts of Haryana, Punjab and the Rann of Kachchh in Gujarat.

• Cropped land (bright red) and waterlogged land (mottled black): canal-irrigated plains of Punjab and Haryana.

• World, Landsat (USA):

• Landsat FCCs use the NIR, red and green bands (MSS bands 7, 5, 4 or 6, 5, 4), and vegetation appears red [4][5].

• Landsat-1 (first named ERTS-1) was launched on 23 July 1972 with an 80 m MSS sensor [4].

• The same standard scheme is used worldwide, so an Indian and a US FCC can be read the same way.

Don't confuse with

• Natural colour composite (NCC): it shows bands in their true colours and looks like a normal photograph, so vegetation looks green. In standard FCC, vegetation looks red [3].
• Clear water vs turbid water in FCC: clear water is dark blue to black. Turbid (silty) water is light blue, because silt reflects green light, which is shown as blue.
• Fallow land vs cropped land: fallow land (bare soil) is light blue to white. Cropped land is bright red. Both can be the same field in different seasons.
• Evergreen vs deciduous forest: evergreen is red to magenta. Deciduous is brown to red, because seasonal leaf fall lowers NIR reflection.

Prelims Hooks

• Standard FCC: green → blue, red → green, NIR → red. So healthy vegetation looks red.
• The colour of vegetation comes from NIR, not from the green band. Healthy leaves reflect NIR strongly and chlorophyll absorbs red light.
• Match: clear water, dark blue to black; turbid water, light blue; waterlogged land, mottled black; dense built-up area, dark blue to bluish green.
• Match: cropped land, bright red; evergreen forest, red to magenta; deciduous forest, brown to red; fallow land and sand/salt-affected land, light blue to white.
• Bhuvan shows some data as NCC by default and allows a switch to FCC [3].
• Trap: "In FCC, vegetation appears green." Wrong. Green vegetation is what you see in NCC.

Mains Points

• FCC-based land-use mapping for land reclamation (GS-I / GS-III):
• Red tones show the health of crops and forests.
• Light blue to white shows salt-affected and fallow land. Mottled black shows waterlogging.

• Together these help plan land reclamation in canal-irrigated areas such as Punjab and Haryana.

• Disaster and resource monitoring (GS-III):

• Light blue turbid water marks silt-laden flood rivers such as the Ganga and Brahmaputra. This helps map flood spread and damage.

• Pixel size has fallen from 80 m (Landsat, 1972) to 23.5 m (LISS-III) [4][2]. So FCCs now show crop and forest health field by field.

• Open data and skills:

• Free LISS-III data on Bhuvan [2] and the open-access aim of the National Geospatial Policy 2022 [7] lower costs for states, researchers and start-ups.
• FCC still needs trained interpreters. Computers classify large areas fast, but people are needed to read colour together with pattern and association.

Related concepts

• Aerial photograph
• Digital image
• Pixel
• Digital number
• Digital image processing
• Visual image interpretation
• Elements of visual interpretation
• Tone
• Texture
• Shadow in image interpretation

Read more

• Data products and image interpretation