// Copyright 1996 - 2004 Landcare Reasearch
//
// Carbon Calculation functions
//
// see CarbonCalc.aspx.vb for further comments
//

function CalculateAnnualCarbonRate( yearOfReversion, annualRainfall, fertility )
{
    //Calculation using national Gompertz equation    
    annualCarbonRateY0 = 2.93 * Math.exp((0.46 * (1 - Math.exp(-0.1 * (yearOfReversion - 1)))) / 0.1);
    annualCarbonRateY1 = 2.93 * Math.exp((0.46 * (1 - Math.exp(-0.1 * yearOfReversion))) / 0.1);
    
    //Calculate annual increment
    annualCarbonRate = annualCarbonRateY1 - annualCarbonRateY0;
    
    //Adjust for Gisborne growth conditions, about 300 t CO<sub>2</sub>/ha at age 37,
    //compared with national values of 276 t CO<sub>2</sub>/ha at the equivalent of a
    //"medium-high" fertility rating.
    
    annualCarbonRate = 1.09 * annualCarbonRate;
    
    //Adjust for user-entered rainfall
    annualCarbonRate = annualCarbonRate - ((1500 - annualRainfall) / 100 * 0.05) * annualCarbonRate;
    
    //Adjust for user-entered fertility rating
    annualCarbonRate = annualCarbonRate + (fertility - 3) * 0.06 * annualCarbonRate;
    
    return annualCarbonRate;
}

function CalculateAnnualGrossMargin( annualCarbonRate, carbonPrice )
{    
    //Calculate annual gross margin for carbon farming
    annualGrossMargin = annualCarbonRate * carbonPrice;
    
    return annualGrossMargin;
}