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Right CHOICE is (a) Star brightness

The EXPLANATION is: The threshold level of star detection is a FUNCTION of star brightness and noise variance and is PERFORMED on subsum of pixels of a size to contain star IMAGE.

Right answer is (a) CCD

The EXPLANATION: The use of CCD arrays allows a small instantaneous field of view for SKY BACKGROUND, for improved signal to noise ratio, while maintaining a large telescopic field of view.

Right choice is (C) Charge coupled devices

The best explanation: The photovoltaic or photoconductive detectors are PACKAGED as charge coupled devices. These can produce an array of SMALL cells or pixels. CCD is a CLOSELY SPACED monolithic array of metal insulator semiconductor capacitors.

Correct answer is (a) Quantum efficiency

The best EXPLANATION: Only a certain number of PHOTONS arriving at the detector are CONVERTED to signal GENERATING ELECTRONS. The quantum efficiency of the detector is defined as the ratio of the photons converted to signal generating electrons to the total number of photons arriving.

Correct choice is (a) True

The EXPLANATION: The night SKY radiance is so low that its effect may be ignored in COMPARISON with star POWER. The day light sky, however, is extremely BRIGHT in comparison with a star. Typically, the sea level sky radiance, 45° from the sun on a clear day is about 2000ft-lamberts.

The correct answer is (d) Intensity of observing star

Easiest explanation: The power from the sky BACKGROUND at the focal PLANE of a telescope depends on the background RADIANCE, the effective entrance AREA, and the FIELD of view of the telescope.

Right answer is (d) SIZE of the star

The explanation is: Star SIGNAL power is the EFFECTIVE area of the telescope TIMES the irradiance of the star. It depends on the spectral irradiance of the STELLAR light, the spectral response of the light detector, and the brightness of the star.

Right answer is (a) True

For explanation I WOULD say: The signal power of a STAR, as seen by a light DETECTOR at the focal plane of the TELESCOPE, is the effective area of the telescope ENTRANCE times the irradiance of the star.

Right option is (a) ANGULAR SIZE of image

The best explanation: The PHYSICAL size of the STAR image depends on the angular size of the image and the EFFECTIVE focal length of the telescope:were d is the physical diameter of the rings in the diffraction image.

Correct ANSWER is (d) f/ NUMBER

Easiest explanation: The ratio of FOCAL length to APERTURE is called the f/ number. For example, an f/10 telescope may have a 30 in. focal length and a 3 in. aperture.

Correct ANSWER is (c) Diffraction limited image

For EXPLANATION: The image of a star at the focal plane of the TELESCOPE with perfect, unobstructed OPTICS is a bright spot surrounded by a series of concentric dark and light RINGS. This image is called a diffraction limited image.

Correct choice is (a) Optical aperture

To explain I WOULD say: Each DESIGN of a telescope is characterized by an optical aperture, an effective focal LENGTH, and a field of VIEW. The optical aperture is the physical DIAMETER of the first element in the telescope.

Correct answer is (c) Catadioptric

Explanation: TELESCOPES are of three types: refractive, which uses lenses as their primary FOCUSING ELEMENTS, reflective, which uses a CURVED mirror for focusing, and catadioptric, which mix mirror and lens systems.

Correct choice is (b) Star catalog

To EXPLAIN I would say: The APPLICATION of Kalman filter begins with the precise MATHEMATICAL definition of the star observation. The inertial line of sight to any GIVEN star is precisely KNOWN from the star catalog.

The CORRECT OPTION is (a) True

For explanation: OBSERVABILITY problems associated with the Kalman filter are greatly intensified in a STELLAR inertial navigation system if the telescope is rigidly mounted to the IMU even THOUGH the IMU is gimballed to provide star pointing.

The correct option is (b) Celestial FIX

Best explanation: Navigators on early TRANSOCEANIC flights used sextants to manually measure STAR angle with RESPECT to their local vertical. Using the line of sights form two or more stars, along with a star catalog and accurate time REFERENCE, the position in Earth latitude and longitude can be deduced. This was known as celestial fix.

The correct ANSWER is (c) Polaris

To explain: The north STAR or Polaris can be used to estimate latitude in the NORTHERN hemisphere using the horizon as a local LEVEL REFERENCE at the observers position. This type of navigation was used by the ancient mariners.

Correct answer is (a) Correction of DRIFT error

Easy explanation: Inertial navigational suffer from drift after long HOURS of using. SINCE the position error growth of these FREE inertial navigation systems was excessive on long flights, it was natural to periodically update their position with position updates from manual STAR fixing.

The correct choice is (B) POSITION and altitude can be measured

For explanation: High precision stellar inertial navigation systems have been DEVELOPED with automatic daylight and NIGHT star tracking system. These are highly useful for military aircraft in that they provide accurate position and attitude information, are autonomous, NON radiation and are invulnerable to jamming.

The CORRECT choice is (b) Triangular

Best explanation: To reduce the ERRORS due to the Doppler shift of the return, a triangular waveform is usually used to modulate the transmitter. Thus a positive Doppler shift will produce a negative frequency ERROR on the rising modulation SLOPE. By averaging the frequency count the error can be MINIMIZED.

The CORRECT OPTION is (c) Receiver low noise AMPLIFIER

To elaborate: The TRANSMITTER power depends on the SENSITIVITY of the receiver. The receiver low noise amplifier typically has a 2 to 3 dB noise figure, resulting in a sensitivity level that allows relatively low transmitter power.

Correct answer is (a) Input power is around 100W

For explanation: The early pulsed radars were evolved to 5W solid state transmitters incorporating receiver pre-amplifiers. They ALSO PROVIDED a high DEGREE of RELIABILITY, low probability of intercept, small size, and high ACCURACY.

The correct choice is (a) 4.2 to 4.4 GHz

The best EXPLANATION: The frequency band of 4.2 to 4.4 GHz is assigned to radar ALTIMETERS. This frequency band is high enough to result in a reasonable small sized antenna to produce 40° to 50° beam but significantly low so that attenuation by RAIN is minimum.

Correct ANSWER is (a) Provide RANGE to the nearest return

Easiest explanation: To provide a range to the nearest return within the BOUNDS of the antenna beam, many modern radar altimeters incorporate the gate in a pulse modulated radar or a FILTER in a frequency modulated radar over the leading EDGE of the return.

The correct answer is (c) Altitude marking radar

The explanation: Altitude marking radar are generally low altitude altimeter designed specifically to PROVIDE MARK signals at SPECIFIC altitudes for initiation of an automatic operation such as fuze TRIGGERING on submunitions or CHUTE opening on lunar landing systems.

Right option is (a) True

Easiest explanation: The important advantage that the Janus configuration has over the non-Janus type is a much LOWER SENSITIVITY of velocity error SINCE the VERTICAL altitude of the aircraft is known.

The correct option is (a) 4

The EXPLANATION is: Although only three beams are required to provide the three components of velocity, most MODERN Doppler radars EMPLOY four beams, because of the PLANAR array antennas generally four such beams. The fourth beam shift can be combined with that of the third to obtain a more accurate component of velocity.

Right option is (a) JANUS

To elaborate: Since the three orthogonal components of velocity are of interest, a minimum of three noncoplanar BEAMS are required to measure the three components. Since such a beam configuration has both forward and rearward looking beams it is CALLED Janus configuration, NAMED after the roman GOD who has the ability to look backward as well as forward.

Right choice is (b) False

The explanation: Helicopters fly at a very slow speed where the conventional pitot TUBE system may fail. In order to measure accurate airspeed below 40 knots, other SYSTEMS such as the Doppler RADAR is used. It is suitable for three dimensional VELOCITY and low velocity measurement, as required for helicopter navigation.

The correct option is (a) DOPPLER shift

Explanation: In Doppler radar, there is a change in reflected frequency when there is RELATIVE motion between the transmitter and the receiver. This change in frequency is CALLED the Doppler shift and is proportional to the relative SPEED between the transmitter and receiver.

The correct option is (b) Transmitter power is high and requires ground assistance

For explanation I WOULD say: The Doppler SYSTEM is self contained, it requires no ground BASED stations or satellite transmitters. The airborne transmitter power REQUIREMENTS are extremely small, which leads to low weight, size, and cost of equipment.

Right choice is (d) Doppler SHIFT

To elaborate: the velocity is determined by MEASURING the Doppler shift of microwave transmitted from the aircraft in several narrow beams POINTED toward the SURFACE at RELATIVELY steep angles, backscattered by the surface and received by the Doppler radar receiver.