Velocity Measurement

Abstract

Velocity is a fundamental parameter of carrier motion.

Appendices

Appendix 6.1: Questions

• 1. Please retrieve and illustrate the ancient and modern speed measurement technology to deepen the understanding of the historical development of speed measurement.

• 2. What are the practical application requirements of speed information? Please briefly describe the important role of speed information in navigation?

• 3. What are the differences in the speed parameters required for the route planning and transfer alignment processes? Analyze the causes.

• 4. Considering the content of this chapter, we briefly describe the classification and related application characteristics of the speed measurement method, such as speed measurement by automobile speed meters. Think about other speed-related principles and formulas in physics, which can they be applied to navigation?

• 5. Please retrieve and illustrate the principle and application of Doppler radar, and compare the similarities and differences with Doppler velocity log.

• 6. Briefly describe the velocity measurement formula of the pit log, and the types and characteristics of the speed measurement device based on the Bernoulli principle.

• 7. Briefly describe the speed measurement formulas of the EM log, DVL and acoustic correlation log, and their working principle and characteristics.

• 8. How can we understand the navigation culture of various countries from the perspective of navigation?

Appendix 6.2: Time thinking in ancient China

China has been attaching great importance to time since ancient times. For example, the term “Sheng Chen Ba Zi” (birth date and the eight characters of a horoscope) indicates the date and time of one’s birthday by sexagenary cycle method. A total of eight characters using celestial stems (“天干 Tian Gan”) and terrestrial branches (“地支Di Zhi”) to represent the year, month, day and time of one’s birth respectively. It used to hold an important position as an old folk belief in China, and now it is often regarded as oriental mysticism or some old superstition. Today with the navigation knowledge we could understand the concept of time in ancient China more fairly and comprehensively.

The year, month, day, and time represented by eight characters indicate the position of the earth in the solar system (year), the position of the earth in the revolution orbit relative to the sun (month), the position of the earth relative to the moon (day), and the angular position of the Earth's rotation relative to the sun (time). Therefore, the term denotes a concept in the domain of modern astronomical time.

It will not be difficult for readers to understand the corresponding position relationship between the time concept (“month, day, time”) and the celestial objects (“sun, earth, month”) in space, but the concept of “year” turns out to be more complicated. Ancient Chinese called Jupiter the year-indicating star, and its revolution period is approximately 12 years (or 11.8618 years). The public regression period of the neighbor planets of the Earth, such as Jupiter and Saturn, is approximately 60 years (or 59.555 years). The movements of Venus, Jupiter, Mercury, Mars, and Saturn relative to the Earth also have cycles, although more complex. The celestial stems and terrestrial branches, or Tian Gan Di Zhi, are associated with periodic changes of celestial bodies in the position relative to the Earth.

As early as the Xia and the Shang dynasties, the ancient Chinese had the sense that “time” and “position” had important influences on the development of things. From the perspective of navigation, the eight characters of birth date reflect the position of the observer in the universe at the birth moment. Behind the position is the combination of position-related factors, such as gravity, magnetic field, light, and temperature, and the like, which in turn affect many extended influences of nature (such as seasons, tides, geological movements, etc.), biology (growth, maturity, aging, etc.), society, and psychology, like the ripples in the lake, layer by layer, stir each other, and pass on indefinitely. Therefore, the interaction of these effects is not merely multidimensional or nonlinear, and the reasons behind are more often than not difficult to clarify and understand. Thus, the ancients considered the far-reaching influence of time in general and used eight characters to represent it as an umbrella term.

Therefore, the birth date in Chinese traditional culture not only partially reveals the spatial and temporal environmental factors of the real world, but also shows the trend of the influence of these factors on people. Due to the probability and bias in the prediction and analysis, in most cases, it is only used as secondary reference in decision making. Nevertheless, when facing the traditional culture different from modern science, we should not simply reject or deny it. Instead, we should analyze the historical influence and essential characteristics behind it with scientific thinking skills.