This algorithm is in development phase and is not used in OBPG data processing.

# Particulate Inorganic Carbon (PIC) - Color Index (CI)

1. Product Summary
2. Algorithm Description
3. Implementation
4. Assessment
5. References

## 1 - Product Summary

This algorithm derives the concentration of particulate inorganic carbon (PIC) in mol m-3, calculated using an empirical relationship derived from in situ measurements of PIC and remote sensing reflectance ($R_{rs}$) in the green-to-red region of the visible spectrum. Algorithm implementation is contingent on the availability of sensor bands near 547 nm and 667 nm. The algorithm is currently available for MODIS-Aqua, and VIIRS-SNPP, from November 2018 onwards.

The algorithm uses the color index approach of Mitchell et al. (2017), which is based on the concept developed by Hu et al. (2012) for calculating chlorophyll-a concentration.

Algorithm Point of Contact: Catherine Mitchell, Bigelow Laboratory for Ocean Sciences

## 2 - Algorithm Description

##### Inputs:
$R_{rs}(\lambda_{green})$ and $R_{rs}(\lambda_{red})$
##### Outputs:
calcite_ci2, the concentration of PIC in $mol$ $m^{-3}$
##### Approach:

The PIC-CI algorithm is a two-band reflectance difference algorithm employing the difference between the Rrs in the green and red bands:

$$CI = R_{rs}(\lambda_{green}) – R_{rs}(\lambda_{red})$$

where $\lambda_{green}$ and $\lambda_{red}$ are the instrument-specific wavelengths closest to 547 and 667 nm.

PIC concentration is then determined via the following empirical relationship:

$$PIC = 0.4579 CI – 0.0006$$

## 3 - Implementation

calcite_ci2
##### Level-2 Product Suite:
None (available through SeaDAS command-line processing)
##### Level-3 Product Suite:
calcite_ci2 (testing product)

## 4 - Assessment

Satellite-to-in-situ validation results are available from the SeaWiFS Bio-Optical Archive and Storage System (SeaBASS). Results are currently not available for calcite_ci2.

Assessment is given in Mitchell et al. (2017).

## 5 - References

Mitchell, C., Hu, C., Bowler, B., Drapeau, D., & Balch, W., M. (2017). Estimating particulate inorganic carbon concentration from ocean color data using a reflectance difference approach. Journal of Geophysical Research. 122, doi: 10.1002/2017JC013146.

Hu, C., Lee, Z., & Franz, B. (2012). Chlorophyll a algorithms for oligotrophic oceans: A novel approach based on three-band reflectance difference . Journal of Geophysical Research, 117(C1). doi: 10.1029/2011jc007395