In remote sensing ,the bandwidth of the Bands used by Microwave sensors is more than those of optical sensors.
Can you clarify what you mean by bandwidth?
Optical bandwidths used in the SPOT satellite sensors range from 40 nm to 220 nm for centre wavelengths between 450 nm and 1640 nm. These correspond to centre frequencies from 667 THz and 184 THz, and spectral bandwidths ranging from 60 THz to 25 THz. http://www.crisp.nus.edu.sg/~research/tutorial/spot.htm
1 cm microwave radiation has a frequency of 30 GHz. The spectral bandwidth available to a microwave sensor will typically be only a fraction of this.
I mean to say that Bands used in optical are very thin when we see the total EMR spectrum where as bands of active microwave remote sensing used by sensors are generally one or two and that is very wide
Can you give some quantitative examples? You seem to be confusing spectral resolution (the ability to separate a narrow range of frequencies of radiation) with spectral bandwidth (the total range of frequencies which are detected).
What do you consider typical mid frequencies and bandwidths used by microwave sensors?
The frequency bands used by AMSR-E (Advanced Microwave Scanning Radiometer - Earth Observing System) vary from 1% to 5% of the centre frequency, distributed rather sparsely over 6 bands from 6.9 GHz to 89 GHz (3.7 octaves) https://nsidc.org/data/docs/daac/amsre_instrument.gd.html
The wavelength bands used by MODIS (Moderate-resolution imaging spectroradiometer) vary from 1% to 5% of centre wavelength in 36 bands with fairly complete coverage of the range 0.4 to 14 micron (5.1 octaves). https://en.wikipedia.org/wiki/Moderate-resolution_imaging_spectroradiometer.
The older SPOT satellite used fewer broader bands (10% centre wavelength) spread over 1.9 octaves.
The relative spectral resolutions (width of each band) are roughly comparable. The MODIS optical sensors cover a very much larger spectral range expressed in GHz, and a somewhat larger range on a logarithmic scale than the AMSR-E microwave radiometer.
For any sensor, the bands selected will depend on the subjects of interest, and what the aim of the sensor is. You may reach different conclusions for other instruments.
There will be differences in detection technology. Silicon photodiodes work well in the visible, but are insensitive to photon energies less than the band gap, so are rarely used for wavelengths longer than 1100 nm. III-V photodiodes (GaAs, GaAlAs, InGaAs, InP, etc) are used at near-IR wavelengths, while InSb is an option for mid-IR wavelengths.
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