Changeset 1712

Timestamp:

03/17/10 17:11:56 (14 years ago)

Author:

Max Voronkov

Message:

added a method to calculate zenith opacity

Location:

trunk/src

Files:

• STAtmosphere.cpp (modified) (2 diffs)
• STAtmosphere.h (modified) (1 diff)

trunk/src/STAtmosphere.cpp

@@ -147 +147 @@
 {
   const size_t result = itsHeights.size();
-  DebugAssert(result > 0, AipsError);
+  DebugAssert(result > 2, AipsError);
   DebugAssert(itsTemperatures.size() == result, AipsError);
   DebugAssert(itsDryPressures.size() == result, AipsError);
@@ -353 +353 @@
 }
 
+/**
+ * Calculate zenith opacity at the given frequency. This is a simplified version
+ * of the routine implemented in MIRIAD, which calculates just zenith opacity and
+ * nothing else. Note, that if the opacity is high, 1/sin(el) law is not correct 
+ * even in the plane parallel case due to refraction. 
+ * @param[in] freq frequency of interest in Hz
+ * @return zenith opacity (nepers, i.e. dimensionless)
+ **/
+double STAtmosphere::zenithOpacity(double freq) const
+{
+  // essentially a numerical integration with the Trapezium method
+  double tau = 0.;
+  for (int layer = int(nLayers()) - 1; layer>=0; --layer) {
+       double dH = 0.;
+       if (layer == 0) {
+           dH = 0.5*(itsHeights[1]-itsHeights[0]);
+       } else if (layer + 1 == int(nLayers())) {
+           dH = 0.5*(itsHeights[nLayers()-1]-itsHeights[nLayers()-2]);
+       } else {
+           dH = 0.5*(itsHeights[layer+1]-itsHeights[layer-1]);
+       }
+       // imaginary part of the total complex refractivity
+       const double nImag = 1e-6*std::imag(dryRefractivity(freq,itsTemperatures[layer],itsDryPressures[layer],
+             itsVapourPressures[layer])+vapourRefractivity(freq,itsTemperatures[layer],itsDryPressures[layer],
+             itsVapourPressures[layer]));
+       tau += dH*4.*casa::C::pi/QC::c.get().getValue()*freq*nImag;
+  }
+  return tau;
+}
+

trunk/src/STAtmosphere.h

@@ -109 +109 @@
   void setWeather(double temperature, double pressure, double humidity);
 
+  /**
+   * Calculate zenith opacity at the given frequency. This is a simplified version
+   * of the routine implemented in MIRIAD, which calculates just zenith opacity and
+   * nothing else. Note, that if the opacity is high, 1/sin(el) law is not correct 
+   * even in the plane parallel case due to refraction. 
+   * @param[in] freq frequency of interest in Hz
+   * @return zenith opacity (nepers, i.e. dimensionless)
+   **/
+  double zenithOpacity(double freq) const;
+
 protected:
   /**