ci: Color Index Algorithm

In BIO-RSG/oceancolouR: Various Functions for Satellite and Data Analysis

Color Index Algorithm

Description

Given blue, green, and red Rrs (remote sensing reflectances), calculate the color index used in Hu et al (2012).

Usage

ci(rrs_blue, rrs_green, rrs_red)

Arguments

rrs_blue	Numeric vector of remote sensing reflectances (Rrs) from the "blue" waveband
rrs_green	Numeric vector of remote sensing reflectances (Rrs) from the "green" waveband
rrs_red	Numeric vector of remote sensing reflectances (Rrs) from the "red" waveband

Details

The blue, green, and red wavebands are 443, 555, and 670, respectively. See ?hu or the example below for details about using sensors with other wavebands.

Value

Numeric vector of color index values

References

Hu, Chuanmin & Lee, Zhongping & Franz, Bryan. (2012). Chlorophyll a algorithms for oligotrophic oceans: A novel approach based on three-band reflectance difference. Journal of Geophysical Research. 117. C01011. 10.1029/2011JC007395.

Link to NASA chlorophyll-a description:

https://oceancolor.gsfc.nasa.gov/atbd/chlor_a/

Examples

# Some in situ chl / MODIS Rrs data used in Clay et al (2019)
in_situ_chl <- c(0.085,0.09,0.1,0.106,0.107,0.122,0.122,0.126,0.128,0.133,0.134,0.143,0.153,0.166,0.166,0.173,0.175,0.182,0.189,0.194,0.197,0.198,0.199,0.208,0.225,0.236,0.249,0.254,0.254,0.258,0.259,0.262,0.266,0.274,0.276,0.28,0.283,0.305,0.311,0.314,0.314,0.318,0.326,0.327,0.34,0.355,0.404,0.405,0.413,0.423,0.435,0.46,0.473,0.493,0.53,0.66,0.66,0.672,0.691,0.726,0.752,0.803,0.803,0.806,0.817,0.829,0.889,0.895,0.897,0.976,1.004,1.006,1.036,1.161,1.219,1.252,1.253,1.835,2.075,2.551,4.117,5.297)
rrs <- matrix(c(0.01042,0.01143,0.00645,0.01166,0.00751,0.00482,0.01019,0.01377,0.00759,0.00724,0.00627,0.00987,0.0101,0.0076,0.00818,0.00637,0.0116,0.00718,0.0091,0.00814,0.0158,0.00721,0.0137,0.00832,0.00442,0.00858,0.01847,0.01217,0.01029,0.00905,0.006,0.01071,0.01411,0.00882,0.00682,0.0096,0.0103,0.00565,0.01648,0.01592,0.01125,0.00791,0.01568,0.01148,0.00789,0.01236,0.00632,0.01144,0.01533,0.0119,0.01201,0.02022,0.00814,0.00768,0.00603,0.00911,0.01096,0.01402,0.00946,0.01063,0.01438,0.01168,0.0117,0.01114,0.01317,0.0099,0.01077,0.00826,0.01352,0.01026,0.01035,0.01166,0.01033,0.01148,0.00933,0.01217,0.01078,0.01174,0.01237,0.00587,0.01591,0.01053,0.00343,0.00407,0.00237,0.00291,0.00323,0.00166,0.00346,0.00377,0.00321,0.00352,0.00281,0.00339,0.0039,0.00357,0.00262,0.00297,0.00358,0.00341,0.00365,0.00331,0.00498,0.00351,0.00499,0.00346,0.00195,0.00361,0.00623,0.00458,0.00348,0.00388,0.00272,0.00458,0.00485,0.00317,0.00313,0.00457,0.004,0.00244,0.00487,0.00597,0.00487,0.00375,0.00578,0.0047,0.00358,0.0035,0.00305,0.00475,0.00558,0.00373,0.00454,0.00624,0.00366,0.00374,0.00268,0.00441,0.00417,0.00431,0.00339,0.00388,0.00476,0.00494,0.00434,0.00476,0.0052,0.00352,0.00461,0.00329,0.00507,0.00431,0.00384,0.00494,0.00441,0.0034,0.0041,0.00477,0.0034,0.00524,0.00518,0.00242,0.00628,0.00384,0.00038,0.00051,0.00023,0.00012,0.00039,2e-05,0.00028,0.00027,0.00028,0.00048,0.00033,0.00029,0.00014,0.00039,9e-05,0.00035,0.00024,0.00031,0.00039,2e-04,0.00054,0.00037,0.00044,0.00033,1e-04,0.00048,0.00065,0.00033,0.00029,0.00053,2e-04,0.00065,0.00051,0.00033,0.00025,0.00067,0.00055,0.00015,0.00034,0.00066,0.00047,0.00038,6e-04,0.00029,0.00044,0.00019,0.00038,5e-04,0.00082,0.00019,0.00058,0.00042,0.00041,4e-04,0.00022,0.00068,0.00032,0.00045,0.00025,0.00015,0.00031,0.00034,0.00065,5e-04,0.00074,0.00048,0.00061,0.00051,0.00037,0.00048,0.00023,0.00032,0.00049,0.00049,0.00052,0.00034,0.00051,0.00031,0.00119,0.00039,0.00061,0.00022), ncol=3)
colnames(rrs) <- c("Rrs_443", "Rrs_547", "Rrs_667")
rrs_blue <- rrs[,1]
rrs_green <- rrs[,2]
rrs_red <- rrs[,3]
# get wavebands of selected sensor, and coefficients from the 2019 Hu paper
wave <- get_ci_bands("modisaqua")
coefs <- get_ci_coefs(2)
# if green waveband is not 555nm, convert green Rrs to Rrs at 555nm
if (wave[2] != 555) {
    rrs_green <- conv_rrs_to_555(rrs_green, wave[2])
}
ci_result <- ci(rrs_blue, rrs_green, rrs_red)

BIO-RSG/oceancolouR documentation built on Feb. 2, 2025, 2:01 a.m.