PART ONE: Design, launch, and operate optical Earth Observation Missions

 

SPATIAL ACCURACY

RADIOMETRIC ACCURACY

SPECTRAL ACCURACY

TEMPORAL ACCURACY

Effective Aperture Diameter

Larger aperture results in a higher diffraction limit which will directly impact MTF.

The larger the aperture area or, the smaller the F#, the more photons the signal can be captured.

The effective aperture of the system determines the optical transmission, which is a function of wavelength.

The effective aperture, including the effect of an obscuration, directly impacts the size of the field area and, therefore, the swath.

Focal Length

GSD scales indirectly with focal length; F# scales directly with focal length. [GSD = Orbital Height x Pixel Pitch / Focal Length]

Focal length directly impacts F#, indirectly impacting the number of photons captured per exposure time.

Limited to no impact on spectral accuracy.

The focal length impacts the swath for pixel pitch and detector size.

F-number

The focal length-to-diameter ratio impacts the MTF, GRD, and SNR.

A lower F# increases the radiometric accuracy for a given system.

Limited to no impact on spectral accuracy.

Little to no effect on temporal accuracy.

Pixel Pitch

The pixel size and GSD are directly proportional—the smaller the pixel smaller the GSD, but the higher the spatial Nyquist Frequency.

Smaller pixels result in a smaller full-well capacity and directly impact the dynamic range and the signal saturation levels.

The pixel size and photodiode technology directly impact the QE, which affects the overall spectral response.

The pixel pitch and the number of pixels determine the instrument’s GSD and swath width. They are increasing the swath results in higher temporal frequency.

Orbit Height

The orbital height has a direct impact on GSD and GRD.

Orbital altitude determines the nadir GSD and directly impacts the instantaneous exposure time.

Limited to no effect on spectral accuracy.

Orbital parameters have a direct impact on the satellite swath and revisit time.

Wavelength

Longer wavelengths result in lower diffraction limits [MTF, GRD]

The specific wavelength of a photon determines the energy of the photon (E=hc/λ) – The longer the wavelength, the less energy.

The wavelength determines the end-to-end optical system design, response, and performance, influencing spectral accuracy.

Limited to no impact on temporal precision.

Exposure Time

An increase in exposure time has a direct impact on spacecraft stability requirements.

The longer the exposure time, the more photons and electrons can be captured.

It will limit the number of spectral bands captured with a single detector in a specific exposure time.

Little to no impact on temporal accuracy.

Quantum Efficiency

QE has a minimal impact on spatial accuracy.

A higher QE results in more photons converted into electrons.

QE is wavelength depended and may have a direct effect on spectral accuracy. Therefore, the QE must be accounted for to determine the end-to-end spectral response.

Limited to no impact on temporal precision.

# TDI Steps

An increase in # of TDI stages directly impacts spacecraft stability requirements.

The increase in digital TDI stages decreases noise levels, increasing SNR.

Limited to no impact on spectral accuracy.

Little to no effect on temporal precision.

# Bands

Different bands have different diffraction limits. See the effect of longer wavelengths on the diffraction limit.

The number of bands may directly impact the FWHM and the total energy transmitted through the system.

The number of bands, together with the bandwidth, determines the amount of information to be extracted. More bands may be required if the spectral content has a high variation.

Little to no impact on temporal accuracy.

FWHM

Different bands and bandwidths directly impact the system’s diffraction limit and MTF and GRD.

The energy and photons transmitted through the system are proportional to the spectral bandwidth.

The spectral bandwidth determines the slightest variation in spectral content be detected.

Little to no impact on temporal accuracy.

Swath

It may increase the geospatial and geolocation accuracy. However, a wide swath may impact overall MTF performance.

The increase in swath may decrease the total transmittance of the system due to an increase in obscuration size.

Little to no impact on spectral accuracy.

The instrument swath directly impacts the number of satellites required to increase revisit frequency.

# Satellites

It may increase the geospatial and geolocation accuracy.

An increase in the number of satellites directly impacts the radiometric calibration accuracy between satellites.

Spectral calibration between satellites becomes trickier with increased spectral resolution and the number of satellites.

The higher the number of satellites, the lower the revisit time.