Multispectral Camera for Small Satellites
Standard cameras, like those in your mobile phone, are optimised to take pictures that represent, as close as possible, what the eye can see. These cameras make use of a colour filter array, known as a Bayer filter mosaic, with a Red, Green, and Blue (RGB) filter distributed on a matrix of photosensors (pixels).
Commercial cameras use a demosaicing algorithm to interpolate the red, green, and blue values for each pixel to recreate the spectral content for each pixel.
These pretty pictures is great to capture the moment but have limited value when going beyond the detection, identification and classification of objects.
Multispectral Cameras: Going Beyond RGB
Satellites use cameras to gather spatial and spectral data of the earth, identify structures, objects and features within the data. The goal is to recognise, classify and quantify changes. These changes may be of a spatial or spectral nature.
Spectral content is one of the most important parameters when analysing Earth Observation data, as it can provide information beyond what is visible. Multispectral cameras do have the ability to sample the spectral reflectance from an object at multiple wavelengths across a broad spectrum to identify the spectral “footprint” of the object.
The growth of multispectral cameras in space
The launch of the first Corona Satellite in 1960 started the Earth Observation race. These satellites used black and white film technology to capture images from space and were great for reconnaissance behind closed borders during the Cold War.
The launch of Landsat 1 in 1972 initiated the civilian use of satellite Earth Observation data for scientific and explorations studies. The Multispectral Camera onboard Landsat 1, called the Multispectral Scanner System (MSS), paved the way for other satellites. The four spectral bands used on this satellite, green, red and two Near-IR bands, became the international standard for satellites. These spectral bands also enabled the scientific community to develop multiple vegetation index algorithms to analyse and classify imagery.
Today, Landsat 8 is designed with eleven spectral bands covering the visible, near-IR, Short Wave Infra-red and thermal infrared bands. Most satellite imagers reflect the trend of using multispectral cameras with multiple spectral bands. These satellites include Sentinel-2, the WorldView Satellites, QuickBird and even the Planet Dove range of satellites.
Multispectral Camera Band Applications
Multispectral cameras with Blue, Green, Red, Red Edge and Near-IR bands are used for multiple applications to provide an overall look at the landscape’s health.
- Central Wavelength: 490 nm
- Range: 450 nm to 520 nm
- Readily absorbed by chlorophyll in plants.
- Provides good penetration of water.
- Less affected by atmospheric scattering and absorption compared to the Coastal Blue Band.
- Sensitive to vegetation senescing, carotenoid, browning and soil background.
- Can be used for atmospheric corrections.
- Central Wavelength: 560 nm
- Range: 542 nm to 578 nm
- Able to focus more precisely on the peak reflectance of healthy vegetation.
- Ideal for calculating plant vigour.
- Very helpful in discriminating between types of plant material when used in conjunction with the Yellow band.
- Sensitive to total chlorophyll in vegetation.
- Central Wavelength: 665 nm
- Range: 650 nm to 680 nm
- Better focused on the absorption of red light by chlorophyll in healthy plant materials.
- Important bands for vegetation discrimination.
- Very useful in classifying bare soils, roads, and geological features.
- Maximum chlorophyll absorption.
- Central Wavelength: 705 nm
- Range: 697 nm to 712 nm
- Centered strategically at the onset of the high reflectivity portion of vegetation response.
- Sensitive to changes in plant eco-physiological status, particular to parameters such as leaf area index (LAI) and leaf chlorophyll content (Cab).
- Central Wavelength: 740 nm
- Range: 732 nm to 748 nm
- Measures the shift of the red edge of leaf reflectance to shorter wavelengths (Blue Shift)
- Central Wavelength: 783 nm
- Range: 773 nm to 793 nm
- It is situated on the upper end of the Red-Edge to monitor the shift in reflectance to shorter wavelengths and the drop in Near-IR reflectance.
- Central Wavelength: 842 nm
- Range: 785 nm to 900 nm
- Very useful for the estimation of moisture content and plant biomass.
- Effectively separates water bodies from vegetation, identifies types of vegetation and also discriminates between soil types.
- It is useful to calculate the Leaf Area Index (LAI).
The MultiScape100 CIS Spectral Bands
This MultiScape100 CIS brings 7 bands across the visible and near-infrared spectrum to the xScape100 family. This multispectral camera is ideal for a wide range of applications within the vegetation monitoring domain, such as agriculture and forestry. The Figure below shows the relative spectral response of the filter bands. These bands are inline with Sentinel-2 bands two to eight.
Feel free to contact us to discuss your multispectral camera needs.
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