ts/wf/cross [WP]: define handling of sample times

src/ts/wf/cross.cc

@@ -103,10 +103,38 @@ int main(int iargc, char* argv[])
     "--xhelp      print details on supported I/O formats\n"
     "\n"
     "The first trace read will be taken as a reference. All other\n"
-    "traces will be cross-correlated with the reference." "\n"
+    "traces will be cross-correlated with the reference or convolved\n"
+    "with the reference. Convolution and cross-correlation are understood\n"
+    "as an approximation to the corresponding integral form. Consequently\n"
+    "the sampling interval of time series must be identical and the\n"
+    "result of the discrete operation will be scaled with the sampling\n"
+    "interval." "\n"
+    "\n"
+    "Data time will be handled as follows:\n"
+    "\n"
+    "Convolution\n"
+    "  The reference series is understood as the impulse response of a\n"
+    "  filter which s to be applied to the other input series. If a\n"
+    "  source date is given in the file of the reference trace, this will\n"
+    "  be taken as the origin of time, allowing for acausal impulse\n"
+    "  response. If it is missing, the first sample of the reference (filter\n"
+    "  impulse response) is understood to be at lag=0s. The date of the\n"
+    "  first sample of the output trace is set to account for possible\n"
+    "  acausal parts of the filter response. Source definition is taken\n"
+    "  only from the first of the input files and is passed unaltered to\n"
+    "  the output.\n"
+    "\n"
+    "Cross-correlation\n"
+    "  Each input trace is cross-correlated with the reference trace.\n"
+    "  When calculating the lag time, absolute time of the first sample\n"
+    "  of each of the traces is taken into account. Absolute time of the\n"
+    "  output is set with respect to the source time. The source time is\n"
+    "  taken from the file header of the reference trace. If a source time\n"
+    "  is missing there, it will be set to a default value.\n"
     "\n"
     "If option -convolve is selected, all traces will be convolved with\n"
     "the reference trace.\n"
+    "\n"
   };
 
   // define commandline options