Syntax_KK
Syntax for the -KK optical calibration argument

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1 - NO NEED for field data, nor for atmospheric correction
2 - this is demonstrated in this website, using a variety of hyper/multi spectral data
 
Requirements are
1 - homogeneous water body and atmosphere
2 - some coverage of optically deep water
3 - some coverage of dry land
 
Problems are
1 - the precision on estimated depth is found wanting, because the noise-equivalent change in radiance  of accessible data is too high for shallow water column correction work 
2 - radiance data should be preprocessed by the provider at level 1 in order to improve S/N ratio
3 - exponential decay: the deeper/darker the bottom, the poorer the performances
 
So
I keep digging
until suitable data
become available
 
 
Syntax_K
  • -KK/1_2_0.50/Knir4.500/CoefK_0.0/Bm400_BG520_GR620_RN700/mask_3
  • -KK/bWLI_bWLJ_KIKJ/Knir/CoefK/BlueMin_BlueGreen_GreenRed_RedNir/FreeComment
  • -KK/1_2_0.50/Knir4.500/CoefK_1.0/Bm400_BG520_GR620_RN700/mask_3/tmnov
  • -KK/1_2_0.50 
    • 1_2         Bands I=1 and J=2 for optical calibration by Jerlov's table of attenuation coefficients 
    • 0.50        Ratio of attenuation coefficients for these two bands I and J: KIKJ=0.50
  • Knir4.5            Attenuation coefficient Knir for the NIR band (set to 4.5 m-1 here)
  • CoefK_1.0              offset applied to Jerlov's K: 
    • default=0 
    • Jerlov's K are offset/decreased as follows: K=K*(1-CoefK)
    • see 4SM_2K_Jerlov
  • Wavebands
    • 450     BlueMin wavelength in nm to start wavebands for modeling
      • is not compulsory: defaults to 450 nm
      • wavebands at wavelengths <BlueMin are skipped while modeling
    • 500    BlueGreen         Wavelength in nm to separate Blue_bands from Green_bands
      • BlueMin<Blue bands<=BlueGreen
    • 640   GreenRed          Wavelength in nm to separate Green_bands from Red_bands
      • BlueGreen<Green_bands<=RedNir
    • 700   RedNir                Wavelength in nm to separate Red_bands from Nir_bands
      • RedNir<NIR_bands
  • ZoneKiKj    Zone for measurement of optical properties: this comment is free and optional

   

 
HowTo SPECTRAL K

K[green]/K[red]=0.277: try other values for  K[green]/K[red] like 0.25 or 0.35
make your decision on what seems to be the best visual fit of the BPL with BPL pixels
What value for
Knir?
towards a quasi-absolute calibration  

HowTo SPECTRAL K

K[green]/K[red]=0.277: try other values for  K[green]/K[red] like 0.25 or 0.35
make your decision on what seems to be the best visual fit of the BPL with BPL pixels

Which value for Knir?
towards a quasi-absolute calibration
 

  • Jerlov's data are provided in the range 400 to 700 nanometers, by steps of 25 nm,
    • for clear Oceanic Waters and Coastal Waters, free of heavy suspended load
  • KWLi and KWLj          are estimated from Jerlov's data using the ratio KWLi/KWLj=0.277
    • observed in the image for wavelengths 550nm  and 650 nm
    • this specifies an intermediate curve among Jerlov's curves: type ~C1
      • Kother_visible_bands
      • from the complete set of ratios Ki/Kj observed in the image
      • and one of  KWLi=0.247 m-1 or KWLj=0.893 m-1
Outdated
  • Knir the NIR band is not covered by Jerlov's data
    • default: by default, Knir  is set to the value which appears in the -KK  argument.
      • i.e. Knir=4.42 m-1   here
    • -CP: if a calibration pixel, which is valid for the NIR band  is provided in the -CP argument,
      • "valid" is to mean: "with a significant bottom contrast Ls-Lsw"
      • then 4SM derives a value for Knir  that is consistent with the complete series of Ki/ Kj  ratios observed in the image among all bands.
  • look in tarawa-subset_m0.cal    for a suitable set of values
    • -CPf0159.0/100.0/015.0 may be selected
    • this yields Knir =4.506  m-1
    • this value shall be used by 4SM instead of the value provided in the commandline
    • the pixel selected yields a depth of 0.70 m in the calibration
    • yes, try it: enable a -CP... argument, and see for yourself in the calibration plot
  • See that this entails a value of  K1/K2=0.3376 and a bad fit of the BPL model
    • adjust the values in -CPf159.0/100.0/015.0, so as to get a good fit of the BPL in the Green/Red pair
    • we need to disable the existing argument and make a new one
    • we can 
      • either reduce the Red value
      • or increase the Green value 
      • or both
      • while aiming at a satisfactory fit with a slope K1/K2=0.30
    • see that -CPf161.0/098.0/015.0 yields 
      • a good fit of all three BPL models
      • K1/K2=0.3016 with water type ~OIII+0.22
      • KNir=4.303
    • enable that value
 
CoefZ in the -Z argument
all K values  in the visible range are divided by CoefZ prior to any computation.
  • If CoefZ!=1.0 , like 1.387 or 1.0001 or 0.9999 or 0.8736..., 
    • then 4SM applies it to all computed depths in all circumstances
    • this is how to accomodate a seatruth-derived depth correcting factor
  • This not compatible with a -CP... argument though
    • therefore if a -CP... argument is enabled, 4SM makes CoefZ=1.0000000 
      • so that the following may take place
  • If CoefZ==1.000000000
    • and a calibration pixel, which is valid for the NIR band, is provided in the -CP argument,
    • then  a new CoefZ is computed (as CoefZ=4.288/4.42=0.9701 in our case)
    • and applied to all computed depths: this is noted in the calibration diagram.
  • To the extent that  K850  would appear to be stable at ~=4.4 m-1 whatever the water type 
    • still to be confirmed,
    • the combined use of the -CP argument and actualized CoefZ 
    • amounts to a quasi-absolute_calibration of spectral K  
    • which may be controlled through the Knir  value provided in the -KK argument.
 
  • This is fairly heavily dependent though on the deep water radiances adopted through the -deglint argument: for example
    • if Lsw 3=  9  ==> K 1=0.2549     K 2=0.8932 CoefZ=0.930  Z=12.2 m at  pixel 469/562   
  • if Lsw 3=10  ==> K 1=0.2554     K 2=0.8933 CoefZ=0.971   Z=12.6 m at pixel 469/562
  • if Lsw 3=11  ==> K 1=0.2559     K 2=0.8934 CoefZ=1.020   Z=13.2 m at pixel 469/562