9.23 Measurement of polar ice thickness. A significant effect of global warm- ing is the thinning of the polar ice, whic

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9.23 Measurement of polar ice thickness. A significant effect of global warm- ing is the thinning of the polar ice, which in turns affects weather and marine life. To assess the condition of the polar ice, a down-looking pulsed radar flies at a height ʼn and transmits a series of pulses at a given repetition rate. The principle of pulsed radar is that it transmits a short pulse and then "listens" to reflected pulses over a period of time before the next pulse is transmitted. Each pulse is 10 µs wide and during that time the radar trans- mits a sinusoidal signal at 3 GHz. The pulses repeat at intervals of 50 µs. The radar receives reflections from the surface of the ice and from the sur- face of seawater under the ice. The processing unit of the radar measures the time delay between the launch of a pulse to the reception of the first reflection as At₁ 3,325 2 ns and to the second reflection as At₂ = 3,384 ± 2 ns. Properties of ice are permeability is µo [H/m], permit- tivity 3.5% [F/m], and conductivity o = 2x10-6 S/m. Properties of air are: uo [H/m], co [F/m] and conductivity o = 107 S/m. Properties of seawater are: uo [H/m], 24 &o [F/m], o = 4 S/m. (a) Calculate the thickness of ice and the maximum error expected. (b) Given a known, fixed flying height of h = 1,000 m, what is the max- imum ice thickness the radar can measure? = (c) If the maximum ice thickness expected is d = 8 m, what is the maximum height the plane can fly and still be able to measure the ice thickness?
584 Sensors, actuators, and their interfaces (d) Given the properties of the various media and the results in (a) calcu- late the magnitude of the electric field intensity of the received pulses if the electric field intensity of the transmitted pulse is 840 V/m. (e) Discuss the possible issues and errors associated with this type of measurement.