Simulation for Case 1 Water

1
Simulation for Case 1 Water

• Deepak Mishra
• Ocean Optics Course (2004)

2
Forward Technique

• Simulation started by creating a depth profile of
• chlorophyll and assuming that the water body is
• Case 1, i.e. chlorophyll bearing phytoplankton
• and their covarying by-products are dominant in
• determining the IOPs of the water.

3
Chlorophyll Profile
4

• The total absorption coefficient a(z?) is
  obtained from
• Prieur-Sathyendranath (1981) model upon
  substitution of
• the assumed C(z) profile.
• The model is given by
• where,
• aw and ac are absorption by pure sea water and
• chlorophyll specific absorption coefficient
  respectively.
• (Taken from Prieur and Sathyendranath, 1981)

5
a)
a) a(z?) as a function of depth for selected
wavelength
b)
b) a(z?) as a function of wavelength for
selected depth
6

• The total scattering coefficient b(z?) is
  obtained from
• Gordon-Morel (1983) model upon substitution of
• the assumed C(z) profile.
• The model is given by

7
a)
a) b(z?) as a function of depth for selected
wavelength
b)
b) b(z?) as a function of wavelength for
selected depth
8
Beam attenuation coefficient c(z?)
a)
a) c(z?) as a function of depth for selected
wavelength
b)
b) c(z?) as a function of wavelength for
selected depth
9
Albedo of single scattering ?o(z?)
a)
a) w0(z?) as a function of depth for selected
wavelength
b)
b) w0(z?) as a function of wavelength for
selected depth
10
Spectral downward and upward plane irradiances at
selected depth
11
Irradiance Reflectance
12
Water leaving radiance and Remote sensing
reflectance
13
PAR
14
Inversion Technique

• IOPs (absorption and backscattering coefficients)
  from AOPs (Kd an d Rrs)
• Gordon, et al. (1988) showed that for Case 1
  waters, R/Q ratio can be useful to exploit the
  theoretical relationship between the Rrs and the
  inherent optical properties, specifically bb and
  a.
• R Irradiance reflectance
• Q Eu/Lu, provides information about the angular
  distribution of the upwelling light field

15
Gordons approximation

• For Case 1 waters
• Rrs 0.54(R/Q)
• R/Q 0.095 (bb /(abb))
• R/Q 0.11(bb/Kd)

16
IOP retrieval (absorption coefficient)
17
Absorption coefficient comparison
18
Backscattering coefficient
19
Chlorophyll retrieval

• Chlorophyll was retrieved from Kd using a
  bio-optical model given by Morel (1988)
• Where and are statistically derived
  functions that convert the chlorophyll
  concentration in mg m-3 to Kd values in m-1.

20
Chlorophyll retrieval
21
Comparison
22
Summary

• There can be considerable error in Rrs from an
  improper removal of sea surface reflectance
  effect.
• Based upon 1 of EPAR surface value depth of
  euphotic zone was found to be 19.8m.
• Semi-analytical inversion algorithms, applied on
  Rrs spectra were able to retrieve chlorophyll
  concentration and IOPs such as absorption
  coefficient, backscattering coefficient.

23
Thank you!!