1. METR 5970.002 Advanced Atmospheric Radiation Dave Turner Lecture 4

4. Reflection and refraction ΘtΘt Θ N1N2N1N2 Θ relative index of refraction Θ angle of incidence Θ t angle of refraction of the transmitted wave Discontinuity in N: EM wave partially reflected and transmitted Refraction means change of propagation direction of the transmitted wave through change of phase velocity partial reflection N 1 = 1 (air) N 2 = 1.33 (water)

5. Refraction Fig. 4.3 Petty (2006) Snell’s law  ray is refracted towards the optically thicker medium follows from Maxwell’s equations for a plane wave with suitable constraints on magnetic and electric fields at the boundaries N 1 = 1 (air) N 2 = 1.33 (water) Snell’s law

6. Total reflection n 2 <n 1 Refraction away from the normal  critical angle for total reflection (Θ 2 =90°) Θ > Θ C total internal reflection within the medium Θ C also maximum transmitted angle at an incident angle of 90° Wikipedia N 1 = 1 (air) N 2 = 1.33 (water) Θ C = 49° Mirages are explained by this

7. Reflection Fig. 4.3 Petty (2006) N 1 = 1 (air) N 2 = 1.33 (water) specular reflection: ray is reflected like elastic ball thrown at floor angle of incidence = angle of reflection surface irregularities much smaller than wavelength (homogeneous surface) inhomogeneous surfaces

8. 8 Rainbow 2cnd rainbow due to double reflection 8

9. GPS Radio Occultation At radio wavelengths (lambda ~ 1 m), the refractive index is function of temperature and humidity

11. Forward Single Scattering Probe (FSSP)

12. HeNe laser illuminates particles passing through center of probe “Dump spot” removes any signal within 4° of laser path through instrument Detector is sensitive to intensity of scattered light within 12° of laser path Integrated signal is function of size of particle (assume water spheres to convert)

13. Log10 (Signal) [arbitrary units]

15. Liquid water with m = 1.155 – 0.982i