Читать книгу Introduction to the Physics and Techniques of Remote Sensing - Jakob J. van Zyl - Страница 35

1 2.1 In order to better visualize the relative scale of the waves' wavelength in different regions of the spectrum, assume that the blue wavelength (λ = 0.4 μm) is expanded to the size of a key hole (1 cm). What would be the wavelength size of other spectra regions in terms of familiar objects?

2 2.2 The sun radiant flux density at the top of the earth's atmosphere is 1.37 kilowatts/m2. What is the flux density at Venus (0.7 AU), Mars (1.5 AU), Jupiter (5.2 AU), and Saturn (9.5 AU)? Express these values in kilowatts/m2 and in photons/m2 sec. Assume λ = 0.4 μm for the sun illumination. (Note that AU = astronomical unit = Earth/sun distance.)

3 2.3 Assuming that the sun emittance spectrum follows exactly Planck's formula:with T = 6000 K. Calculate the percent of solar energy in the following spectral regions:In the UV (λ < 0.4 μm)In the visible (0.4 μm < λ < 0.7 μm)In the infrared (0.7 μm < λ < 10 μm)In the thermal infrared and submillimeter (10 μm < λ < 3 mm)In the microwave (λ > 3 mm)

4 2.4 The amplitudes of two coexistent electromagnetic waves are given byDescribe the temporal behavior of the total electric field E = E1 + E2 for the following cases:Repeat the exercise for A = 2B.

5 2.5 The amplitudes of two coexistent electromagnetic waves are given bywhere c is the speed of light in a vacuum. Let ω′ = ω + Δω and Δω ≪ ω. Describe the behavior of the power of the composite wave as a function of P1 and P2 of each individual wave.

6 2.6 A plasma is an example of a dispersive medium. The wavenumber for a plasma is given bywhere c = speed of light and ωp= plasma angular frequency.Calculate and plot the phase and group velocity of a wave in the plasma as a function of frequency.Based on the results of (a), why is a plasma called a dispersive medium?

7 2.7 A radar sensor is carried on an orbiting satellite which is moving at a speed of 7 km/sec parallel to the earth’s surface. The radar beam has a total beam width of θ = 4° and the operating frequency is ν = 1.25 GHz. What is the center frequency and the frequency spread of the echo due to the Doppler shift across the beam for the following cases:a nadir‐looking beama 45° forward‐looking beama 45° back‐looking beam

8 2.8 Repeat Problem 2.7 for the case where the satellite is moving at a velocity of 7 km/sec but at a 5° angle above the horizontal.

9 2.9 Plot and compare the spectral emittance of black bodies with surface temperatures of 6000 K (Sun), 600 K (Venus), 300 K (Earth), 200 K (Mars), and 120 K (Titan). In particular, determine the wavelength for maximum emission for each body.

10 2.10 A small object is emitting Q watts isotropically in space. A collector of area A is located a distance d from the object. How much of the emitted power is being intercepted by the collector? Assuming that Q = 1 kW and d = 1000 km, what size of collector is needed to collect 1 milliwatt and 1 microwatt?

11 2.11 Two coexistent waves are characterized byDescribe the behavior of the total wave E = E1 + E2 for the cases where α = 0, α = π/2, α = π and α a random value with equal probability of occurrence between 0 and 2π.