FC - Cameras_I

Forty question-and-answer flashcards covering CCD/APS sensors, optics, imaging geometry, calibration, and related physical principles from the lecture on planetary cameras and geodesy.

What does the abbreviation "CCD" stand for in digital imaging?

Charge-Coupled Device

In which professional fields are CCD sensors especially common because they provide high-quality image data?

Professional, medical, and scientific applications

Name three key advantages of CCDs over many other imaging technologies.

Excellent linearity, high sensitivity, and very good geometric stability

Give two traditional advantages of photographic film when compared with CCDs.

Very large dynamic range and extremely high resolution

What is meant by a CCD pixel’s "full-well capacity"?

The maximum number of photo-generated electrons the pixel (bucket) can hold before it saturates

Why do large frame CCDs often need a mechanical shutter during read-out?

Because photon flux continues while the array is being emptied, causing smearing unless exposure is blocked

What is meant by the "quantum efficiency" of a sensor?

The percentage of incoming photons that are converted into charge carriers by the detector

For what does "APS" stand, and what is its defining hardware characteristic?

Active Pixel Sensor; each pixel contains its own amplifier

List two practical advantages of APS sensors relative to traditional CCDs.

Lower operating voltage and ability to address/read individual pixels

Pushbroom (line) CCDs create images by exploiting what natural spacecraft property?

The along-track motion of the spacecraft in orbit

High read-out rates (100–1000 Hz) of line CCDs enable what capability?

Acquisition of very large, high-resolution swath images in a single pass

State one common difficulty when using color CCDs in space applications.

Accurate color calibration is difficult (and resolution is partially sacrificed)

What optical quantity does the aperture of a camera primarily control?

The amount of light (light-gathering power) reaching the image plane

Define the focal length of an optical system.

The distance from the center of a lens (or mirror) to the point where parallel incoming rays converge

Give the thin-lens (Lensmaker) equation in its simplified form for focal length f.

1/f ≈ (n − 1)(1/R₁ − 1/R₂)

Write the simple relationship that links ground pixel size (s), detector pixel size (p), range (r), and focal length (f).

s / p = r / f

Using p = 7 µm, f = 175 mm, and r = 250 km, what theoretical ground resolution does the HRSC camera achieve?

Approximately 10 m per pixel

How is the F-number (f/#) of a lens mathematically defined?

F-number N = f / D, where f is focal length and D is aperture diameter

Compare the dynamic range of 8-bit and 16-bit images.

8-bit spans 256 grey levels; 16-bit spans 65 536 grey levels (much larger range)

What phenomenon called "blooming" occurs when a CCD pixel’s full-well capacity is exceeded?

Excess charge spills into adjacent pixels, producing bright streaks or "bleeding"

What drawback do anti-blooming gates introduce even though they suppress blooming?

They lower the pixel fill factor and thus reduce sensitivity and well depth

What does "PSF" stand for in optical imaging?

Point Spread Function

How is the Modulation Transfer Function (MTF) mathematically related to the PSF?

MTF is the Fourier transform of the Point Spread Function

Write the diffraction-limited spot size equation (for small angles).

d = 1.22 λ f / a

For SRC parameters (λ = 500 nm, f = 980 mm, a = 91 mm), what is the calculated diffraction limit?

Approximately 6.6 µm, close to the 9 µm pixel size

What image is taken with zero exposure time and shutter closed to measure electronic read noise?

A Bias Frame

Which calibration frame measures thermally generated signal and reveals "hot" pixels?

The Dark Frame

Which calibration frame is obtained by imaging a uniform bright surface to map pixel-to-pixel sensitivity?

The Flat Field Frame

State the basic sequence for radiometric correction using bias, dark, and flat-field data.

Subtract bias/dark from flat, subtract bias/dark from image, then divide by the normalized flat field

In a 1024 × 1024 pixel CCD (origin at 0.5,0.5), what are the pixel coordinates of the array center?

(512.5, 512.5)

Give the radial distortion model used in geometric calibration of spacecraft cameras.

xd = xu + (k₁r² + k₂r⁴)xu; yd = yu + (k₁r² + k₂r⁴)yu where r² = xu² + yu²

For a spherical mirror, how is focal length related to the mirror’s radius of curvature R?

f = ½ · (2R) → f = R/2 (for a single reflective surface) or simply f = 2R in thin-mirror form

Name one optical side effect of using a very large aperture besides increased light gathering.

Reduced depth of field (also potential aberrations or vignetting)

What major advantage do interline CCDs have over full-frame CCDs?

Very rapid electronic read-out, eliminating the need for a mechanical shutter

In the photoelectric effect, what parameter is proportional to the number of emitted photoelectrons for a given material?

The intensity (brightness) of the incident radiation

What determines the maximum kinetic energy of photoelectrons in the photoelectric effect?

Only the frequency (or photon energy) of the incoming radiation

How does a small pixel size affect image noise and resolution?

Increases spatial resolution but raises noise because of lower full-well capacity

Approximately how much storage does a single-channel 1024 × 1024 8-bit image require?

About 1 Mbyte

Why are CCDs valued in astronomical astrometry and photometry?

Their linear response enables precise brightness and positional measurements