Understanding Reflection and Refraction in Atmospheric Radiation

1. METR 5970.002Advanced Atmospheric Radiation Dave Turner Lecture 4

4. Reflection and refraction • Discontinuity in N: EM wave partially reflected andtransmitted • Refraction means change of propagation direction of the transmitted wave through change of phase velocity N1 = 1 (air) N2 = 1.33 (water) Θ Θ N1 N2 relativeindex of refraction Θt partial reflection Θangle of incidence Θt angle of refraction of the transmitted wave

5. N1 = 1 (air) N2 = 1.33 (water) Refraction Snell’s law • 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 Fig. 4.3 Petty (2006)

6. Total reflection n2<n1 Wikipedia Refraction away from the normal  critical angle for total reflection (Θ2=90°) • Θ > ΘC total internal reflection within the medium • ΘC also maximum transmitted angle at an incident angle of 90° N1 = 1 (air) N2 = 1.33 (water) ΘC = 49° Mirages are explained by this

7. N1 = 1 (air) N2 = 1.33 (water) Reflection • 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) Fig. 4.3 Petty (2006) inhomogeneous surfaces

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. Forward Single Scattering Probe (FSSP) • 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