Module: ETCalculator

Defined in:
lib/asigbiophys/et_calculator.rb

Overview

Calculates adjusted evapotranspiration (hereinafter ET) from a “reference ET” number and other stuff like percent canopy cover or leaf-area index.

Created

31May2011

Authors

P Kaarakka, Rick Wayne

Instance Method Summary collapse

Instance Method Details

#adj_et_from_lai_corn(ref_et, lai) ⇒ Object

Return adjusted ET from the reference ET if the leaf area index is already in hand Crop coeff math is from WI_Irrigation_Scheduler_(WIS)_VV6.3.11.xls



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# File 'lib/asigbiophys/et_calculator.rb', line 65

def adj_et_from_lai_corn(ref_et,lai)
crop_coeff = 1.1*(1-Math.exp(-1.5*(lai)))
adj_et = ref_et * crop_coeff
end

#adj_et_lai_corn(ref_et, days_since_emergence) ⇒ Object

Return adjusted ET from the reference ET and the days sinçe emergence Crop coeff math is from WI_Irrigation_Scheduler_(WIS)_VV6.3.11.xls



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# File 'lib/asigbiophys/et_calculator.rb', line 58

def adj_et_lai_corn(ref_et,days_since_emergence)
crop_coeff = 1.1*(1-Math.exp(-1.5*(lai_corn(days_since_emergence))))
adj_et = ref_et * crop_coeff
end

#adj_et_pct_cover(ref_et, pctCover) ⇒ Object

Return the adjusted ET. Uses regression coefficients derived by J. Panuska from the UW Extension pub A3600.



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# File 'lib/asigbiophys/et_calculator.rb', line 12

def adj_et_pct_cover(ref_et,pctCover)
  ref_et = 0.0 if ref_et == nil
  pctCover = 0.0 if pctCover == nil
  return 0.0 if pctCover < 0.000001
  # regression coefficients from J. Panuska in Linear_Regressions_for_A3600_Table.doc and based on Table C of UW Extension pub A3600, "Irrigation Management in Wisconsin - the Wisconsin Irrigation Scheduling Program (WISP)" 
  coeff = [[0,0],[-0.002263,0.2377],[-0.002789,0.3956],[-0.002368,0.5395],[-0.000316,0.6684],[-0.000053,0.7781],[0.001053,0.8772],[0.001947,0.9395],[0.000000,1.000]]

  #NOTE: coeffIndex and interpolations assume pctCover curves are all exactly 10% apart. 
  coeffIndex = (pctCover/10).floor
  case coeffIndex
    when 0  # Get zero %cover adj_et
      case ref_et
        when 0.0 
          return 0.0  
        when 0..0.159
          adj_etLow = 0.0
        when 0.160..0.319
          adj_etLow = 0.010
        else 
          adj_etLow = 0.020
        end
        # Get 10 %cover adj_et
        adj_etHigh = coeff[1][0] + ref_et*coeff[1][1]
        # Interpolate adj_et between zero and 10 %cover
        adj_et = adj_etLow + ((pctCover/10)*(adj_etHigh-adj_etLow))

    when 1..7  # Get low end adj_et
      adj_etLow  = coeff[coeffIndex][0] + ref_et*coeff[coeffIndex][1]  
      # Get high end adj_et
      adj_etHigh = coeff[coeffIndex+1][0] + ref_et*coeff[coeffIndex+1][1]
      # Interpolate adj_et between low and high %cover
      adj_et = adj_etLow + (((pctCover - coeffIndex*10)/10) * (adj_etHigh-adj_etLow))

    else     # At 80% cover and above there is no adjustment to the ref_et
      adj_et = ref_et
  end
  return adj_et
end

#calc_adj_ET(day) ⇒ Object

Duck Typing at work here; “day” can be anything that responds to the methods: “et_method”, “ref_et”, “leaf_area_index”, and “pct_cover”. So an ActiveRecord class instance with those table columns will work, or a mock object for testing, or wrapper around some other class that calls them referenceET and leafAreaIndex.



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# File 'lib/asigbiophys/et_calculator.rb', line 74

def calc_adj_ET(day)
  if day.respond_to?('et_method')
    day.et_method.adj_et(day)
  else
    raise "Can't get ET method"
  end
end

#lai_corn(days_since_emergence) ⇒ Object

LAI growth curve function for corn from WI_Irrigation_Scheduler_(WIS)_VV6.3.11.xls



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# File 'lib/asigbiophys/et_calculator.rb', line 52

def lai_corn(days_since_emergence)
(0.000000000009*(days_since_emergence)**7.95)*(Math.exp(-0.1*(days_since_emergence)))
end

#linear_increment(start_val, finish_val, n_vals) ⇒ Object 



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# File 'lib/asigbiophys/et_calculator.rb', line 114

def linear_increment(start_val,finish_val,n_vals)
  (finish_val - start_val) / (n_vals - 1)
end

#linear_interpolation(wx_arr, start, finish, entered_method, calc_method) ⇒ Object 



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# File 'lib/asigbiophys/et_calculator.rb', line 118

def linear_interpolation(wx_arr,start,finish,entered_method,calc_method)
  return unless wx_arr && wx_arr.size > 2 # Can't interpolate nothin', or if arr has fewer than 3 values
  return unless (n_vals = 1 + finish - start) > 1 # Finish and start have to be far enough apart
  return if start >= finish && start < 0 && finish > wx_arr.size - 1
  start_val = wx_arr[start][entered_method] || wx_arr[start][calc_method] || 0.0
  finish_val = wx_arr[finish][entered_method] || wx_arr[finish][calc_method] || 0.0
  incr = linear_increment(start_val,finish_val,n_vals)
  start.upto(finish).each do |ii|
    # Note that this sets the calculated_pct_cover fields of the days with entered_pct_cover,
    # but should be to the same value
    wx_arr[ii][calc_method] = start_val + (ii - start)*incr
    if wx_arr[ii].respond_to?('save!')
      begin
        wx_arr[ii].save!
      rescue Exception => e
        dbg = <<-END
        ETCalculator::linear_interpolation: Could not save wx_arr[#{ii}]
          start #{start} finish #{finish} entered_method #{entered_method} calc_method #{calc_method}
          start_val #{start_val} finish_val #{finish_val} incr #{incr}
          #{wx_arr[ii].inspect}
        END
        logger.warn dbg
      end
    end
  end
end

#surrounding(wx_arr, middle, parameter) ⇒ Object

Percent Cover methods



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# File 'lib/asigbiophys/et_calculator.rb', line 91

def surrounding(wx_arr,middle,parameter)
  max_index = wx_arr.size - 1
  return nil if max_index < 2 || middle > max_index || middle < 0
  res = [0,max_index]
  if middle > 0
    (middle - 1).downto(0) do |ii|
      if wx_arr[ii].respond_to?('[]') && (wx_arr[ii][parameter])
        res[0] = ii
        break
      end
    end
  end
  if middle < max_index
    (middle + 1).upto(max_index) do |ii|
      if wx_arr[ii].respond_to?('[]') && (wx_arr[ii][parameter])
        res[1] = ii
        break
      end
    end
  end
  res
end

#update_adj_et_single_day(day) ⇒ Object

In addition to the four methods expected above for “day”, this one expects “day” to have a adj_et=(et_value) method



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# File 'lib/asigbiophys/et_calculator.rb', line 84

def update_adj_et_single_day(day)
  day.adj_et =  calc_adj_ET(day)
end