"Specular reflection from a body of water is calculated by the Fresnel equations.[6] Fresnel reflection is directional and therefore does not contribute significantly to albedo which primarily diffuses reflection."
Spherical zone height calculation
The total amount of the specularly reflected portion of solar flux
Our comment:
The planet solar irradiated area from normal point to the terminator of 90o is gradually increasing in dimensions. The further away on the globe's surface from the point of ZENITH INCIDENCE ANGLE to the larger angles of incidence the more extend in dimensions the spherical zones' areas are.
So the larger angles of incidence are accompanied with much larger areas times the much higher the specular reflection portion outgoing to space from them.
Consequently the Φ = 0,47 and the specular reflection of the "waterworld" sphere is expected to be very much comparable.
End of comment.
In order to demonstrate our thought we shall make the effort, and we shall calculate, for the entire solar lit hemisphere, the total amount of the specularly reflected portion of solar flux, based on the above graph's approximate reading data.
We shall divide the by the solar flux lit entire hemisphere in small surface area spherical zones, by proceeding with small 2,5° steps of the angle of incidence variables.
We shall calculate every spherical zone's area (m²) within every and each of this small angle of incidence change 2,5° steps [ θ°(i+1) - θ°i = 2,5° ]
Then we shall read the approximate values on water surface specular reflectivity graph for every chosen for calculation spherical zone (angle of incidence)
(Reflectance of smooth water at 20°C (refractive index 1.333).)
We shall then calculate the product for every small spherical zone area with the related to the same angle of incidence the local reflectance from graph.
Finally we shall summarize all the resulted 2,5° steps (spherical zones * local reflectance from graph) products, and average the sum over the planet's cross-section area, which is perpendicular to solar flux (the area of the perpendicular incidence).
Surface area of spherical zone
A = 2πrh
r - the radius of a planet
h - the height of a spherical zone
The height "h.i " of a spherical zone "i" at the point of solar flux's angular incidence "θ°i"
h.i = [ r*cos θ°i - r*cos θ°(i+1) ] =
= r [ cos θ°i - cos θ°(i+1) ]
Reflectance of smooth water at 20°C (refractive index 1.333)
Reflectance of smooth water at 20°C (refractive index 1.333).
Water-earth total specular reflection based on the Fresnel reflection
Specular reflection from a body of water is calculated by the Fresnel equations.[6] Fresnel reflection is directional and therefore does not contribute significantly to albedo which primarily diffuses reflection.
The radius of a planet is r
The height " h.i " of a spherical zone " i " at the point of solar flux's angular incidence θ°i is
In the above scheme we explain the spherical zone's height calculation method:
h.i = [ r*cos θ°i - r*cos θ°(i+1) ] =
= r [ cos θ°i - cos θ°(i+1) ]
Analysis of terms.
S - the incident on the planet solar flux (W/m²), perpendicular to the planet's cross-section
r - planet's radius (m)
πr² - planet's cross-section area perpendicular to the solar flux's beams (m²)
N - the normal to the surface
θ° - angle of solar flux's incidence
θ°i - angle of solar flux's incidence at i point
h.i = r [ cos θ°i - cos θ°(i+1) ] - the i spherical zone area height
A.i - spherical zone area m² at point i
A.i = 2πr * ( r*cos θ°i - r*cos θ°i+1 ) - spherical zone area at i point (m²)
A.i = 2πr² * ( cos θ°i - cos θ°i+1 ) (m²)
...........
Spec.i - ( specular reflectivity at point i ) ( specular reflectivity at point i ) taken from graph for the ( θ°i ) angle of incidence
A.i * Spec.i - the total incident on zone Ai area solar irradiation reflected portion m² *W/m² = W
Σ ( Α.ι* Spec.i ) - the Sum total incident on the entire hemisphere's surface solar irradiation reflected portion (W)
Σ ( Α.ι* Spec.i ) /πr² - the total specular reflection portion of the incident solar flux, averaged on the planet's cross-section disk (W/m²)
When substituting terms in the above sentence we would have:
Σ [ 2πr² * ( cos θ°i - cos θ°i+1 ) (m²) * Spec.i W/m² ] /πr² (m²)
When simplifying by eliminating the πr² term
Σ 2 *( cos θ°i - cos θ°i+1 ) * Spec.i (W/m²) - the sphere's total specular reflection portion of the incident solar flux, averaged on the planet's cross-section disk perpendicular to the incoming solar flux
or
2 * Σ [ ( cos θ°i - cos θ°i+1 ) ] * Spec.i (W/m²) (1)
let's symbolize the ( cos θ°i - cos θ°i+1 ) expression with Δcosθ°i term
So we shall write:
2 * Σ Δcosθ°i * Spec.i (W/m²)
Table of data (by 2,5° steps ) and the product ( Δcosθ°i * Spec.i ) results
Angle of
incidence..................cosθ°i - cosθ°i+1 ..graph data.......product
θ°ι...............cos θ°ι.......... Δcosθ°i........Spec.i....... Δcosθ°i * Spec.i
0°......................1.............0,00095..............0....................0
2,5°................0,99905.........0,00285........0,02...............0,00019 5°............0,99619.........0,004750............0,02...............0,000056
7,5°................0,99144.........0,006637......0,02............... 0,000091
10°..........0,98481..........0,0085117............0,02............ 0,000135
12,5°..............0,97630..........0,0104........0,02................ 0,000165 15°..........0,96593............0,01221...........0,02...............0,00020
17,5°..............0,95372...........0,0140...........0,02............. 0,00024
20°..........0,93969............0,0158...........0,02................0,00028
22,5°..............0,92388..........0,0176...........0,02.............. 0,00031 25°..........0,90631............0,0193...............0,02.............0,00035
27,5°..............0,88701...........0,0210........0,02............... 0,00036
30°..........0,86603...........0,0226.............0,02...............0,00042 32,5°..............0,84339...........0,0242..........0,02...............0,000452 35°..........0,81915...........0,0258..............0,02.................0,000484 37,5°.............0,79335...........0,0273.........0,02...............0,000516 40°..........0,76604...........0,0288.............0,02...............0,000546 42,5°.............0,73728............0,0302..........0,023.............0,000662 45°..........0,70711...........0,0315...............0,025...........0,000755 47,5°.............0,67559............0,0329...........0,031............0,00098 50°..........0,64279...........0,0340.................0,035.............0.00115 52,5°..............0,60876...........0,035.............0,037............0,00126 55°..........0,57358..........0,0361.....................0,040.........0,00141 57,5°..............0,53730...........0,0373............0,055............0,00200 . 60°..........0,5....................0,0383...............0,065...........0,00243 62,5°..............0,46175...........0,0391............0,085............0,00325 65°..........0,42262............0,0399.................0,1..............0,003913 67,5°..............0,38268...........0,0407...............0,17...........0,00679 70°..........0,34202.............0,0413................0,22..............0,00895
72,5°..............0,30071..........0,0419...............0,27...........0,01115
75°..........0,25882.......... 0.0424 ...............0,30.............0,01257 77,5°..............0,21644...........0,0428............0,39............0,01653 80°..........0,17365...........0,0431................0,45................0.01926 82,5°..............0,13053...........0,0434.............0,60..............0,02587 85°..........0,08716...........0,0435...............0,70................0,03036 87,5°..............0,04362..........0,0436..............0,82............0,03570 90°...................0...........................................1.............0,04362
Σ....................................................................................0,217
When summarizing from the Table the Δcosθ°i * Spec.i the product results we shall have
Σ Δcosθ°i * Spec.i = 0,217
and multiplying times 2 according to the equation (1) above
2 * Σ Δcosθ°i * Spec.i = 0,217 * 2 = 0,434
- it is the specularly reflected portion of the incident solar flux It is the sphere's total specular reflection portion of the incident solar flux, which is averaged on the planet's cross-section disk.
When considering an oceanic-like planet Earth total reflected energy the diffuse a*So + specular 0,434 *So =
= 0,3 * 1.362W/m² + 0,434 * 1.362W/m² =
= 0,734 * 1.362 W/m² = 999,71 W/m² REFLECTED
and only 1.362 - 999,71 = 362 W/m² "ABSORBED"
This result (362 W/m² "ABSORBED") is in a satisfactory magnitude accordance with the smooth planet surface the solar incident flux's "absorption" ( 444 W/m² not-reflected).
Φ(1 - a)So = 0,47(1 - 0,306)1362 W/m² = 444 W/m² not-reflected
when compared with the blackbody theory the 1.362 * (1 - 0,306) =
= 945 W/m² "ABSORBED"
The difference is more than twice as much!
********
0,434*S specularly reflected from the sea waters...
Now, let's see:
Φ(1- a) *S is the not reflected portion of the incident solar flux.
The sea water Albedo a=0,08
Φ=0,47 for the smooth surface spheres (planets without or with a thin atmosphere)
Φ(1-a)*S = 0,47(1 - 0,08)*S = 0,47*0,92*S = 0,4324*S
it is the not reflected portion of the incident solar flux.
"Because light specularly reflected from water does not usually reach the viewer, water is usually considered to have a very low albedo <b>in spite of its high reflectivity at high angles of incident light</b>.”
(emphasis added)
Link:
https://en.wikipedia.org/wiki/Albedo
Here it is the key point:
"... in spite of its high reflectivity <b>at high angles of incident light</b>."
(early morning, late afternoon, and near the poles)
Sun shines on the Globe all the time. At every given moment there is only one point on the Globe where the angle of incidence is zero.
And, at every given moment there are always the high angles of incident light on the Globe.
So, every given moment the most of the Globe's surface area is at high angles of incident light.
-
The Distinguishly Directional Reflective Constituent
We have multiplied the Φ with the (1 -a)*S ,
so it is Φ*(1- a)*S W/m²
Where:
Φ - is the solar irradiation accepting factor (dimensionless)
a - is the satellite measured Albedo (dimensionless)
S - is the solar flux at the planet's or moon's distance from the sun (W/m²)
The Φ*(1- a)*S (W/m²) is the not reflected portion of the incident on planet or moon surface solar SW EM energy.
The equation is true for all planets and moons ib solar system
Φ = 0,47 is for the smooth surface planets and moons without-atmosphere or with a thin atmosphere, Earth included:
( Mercury, Moon, Earth, Mars, Europa, Ganymede )
those planets and moons have a distinguishly directional reflective constituent, which cannot be "seen" and measured by satellites' sensors.
Φ = 1 is for the rest planets and moons - the rough surface planets and moons, which do not have a distinguishly directional reflective constituent.
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