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+#======================================================================
+#                    W O R K H O R S E U T I L S . P L 
+#                    doc: Wed Feb 12 10:21:32 2003
+#                    dlm: Sun May 23 16:32:37 2010
+#                    (c) 2003 A.M. Thurnherr
+#                    uE-Info: 142 42 NIL 0 0 72 2 2 4 NIL ofnI
+#======================================================================
+
+# miscellaneous Workhorse-specific utilities
+
+# History:
+#	Feb 12, 2003: - created
+#	Feb 14, 2003: - added check for short (bad) data files
+#	Feb 26, 2004: - added Earth-coordinate support
+#				  - added ensure_BT_RANGE()
+#	Mar 17, 2004: - set bad BT ranges to undef in ensure_BT_RANGE
+#				  - calc mean/stddev in ensure_BT_RANGE
+#	Mar 20, 2004: - BUG: find_seabed() could bomb when not enough
+#					bottom guesses passed the mode_width test
+#	Mar 30, 2004: - added &soundSpeed()
+#	Nov  8, 2005: - WATER_DEPTH => Z_BT
+#	May 23, 2010: - Z* -> DEPTH*
+
+use strict;
+
+#======================================================================
+# fake_BT_RANGE(dta ptr)
+#======================================================================
+
+# During cruise NBP0204 it was found that one of Visbeck's RDIs consistently
+# returns zero as the bottom-track range, even thought the BT velocities
+# are good. This functions calculates the ranges if they are missing.
+
+sub cBTR($$$)
+{
+	my($d,$e,$b) = @_;
+	my($maxamp) = -9e99;
+	my($maxi);
+
+	for (my($i)=0; $i<$d->{N_BINS}; $i++) {
+		next unless ($d->{ENSEMBLE}[$e]->{ECHO_AMPLITUDE}[$i][$b] > $maxamp);
+		$maxamp = $d->{ENSEMBLE}[$e]->{ECHO_AMPLITUDE}[$i][$b];
+		$maxi = $i;
+	}
+	$d->{ENSEMBLE}[$e]->{BT_RANGE}[$b] =
+		$d->{DISTANCE_TO_BIN1_CENTER} + $maxi * $d->{BIN_LENGTH};
+}
+
+sub ensure_BT_RANGE($)
+{
+	my($d) = @_;
+	for (my($e)=0; $e<=$#{$d->{ENSEMBLE}}; $e++) {
+		my($sum) = my($n) = 0;
+		if (defined($d->{ENSEMBLE}[$e]->{BT_VELOCITY}[0])) {
+			for (my($b)=0; $b<4; $b++) {
+				cBTR($d,$e,$b)
+					unless defined($d->{ENSEMBLE}[$e]->{BT_RANGE}[$b]);
+				$sum += $d->{ENSEMBLE}[$e]->{BT_RANGE}[$b]; $n++;
+			}
+		} else {
+			for (my($b)=0; $b<4; $b++) {
+				$d->{ENSEMBLE}[$e]->{BT_RANGE}[$b] = undef;
+			}
+		}
+		$d->{ENSEMBLE}[$e]->{BT_MEAN_RANGE} = $sum/$n if ($n == 4);
+	}
+}
+
+#======================================================================
+# (seabed depth, stddev) = find_seabed(dta ptr, btm ensno, coord flag)
+#======================================================================
+
+# NOTE FOR YOYOS:
+#	- this routine only detects the BT around the depeest depth!
+#	- this is on purpose, because it is used for [listBT]
+
+# This is a PAIN:
+# 	if the instrument is too close to the bottom, the BT_RANGE
+#	readings are all out; the only solution is to have a sufficiently
+#	large search width (around the max(depth) ensemble) so that
+#	a part of the up (oops, I forgot to finish this comment one year
+#	ago during A0304 and now I don't understand it any more :-)
+
+my($search_width) = 200;	# # of ensembles around bottom to search
+my($mode_width) = 10;		# max range of bottom around mode
+my($z_offset) = 10000;		# shift z to ensure +ve array indices
+
+sub find_seabed($$$)
+{
+	my($d,$be,$beamCoords) = @_;
+	my($i,$dd,$sd,$nd);
+	my(@guesses);
+
+	return undef unless ($be-$search_width >= 0 &&
+						 $be+$search_width <= $#{$d->{ENSEMBLE}});
+	for ($i=$be-$search_width; $i<=$be+$search_width; $i++) {
+		next unless (defined($d->{ENSEMBLE}[$i]->{BT_RANGE}[0]) &&
+					 defined($d->{ENSEMBLE}[$i]->{BT_RANGE}[1]) &&
+					 defined($d->{ENSEMBLE}[$i]->{BT_RANGE}[2]) &&
+					 defined($d->{ENSEMBLE}[$i]->{BT_RANGE}[3]));
+		my(@BT) = $beamCoords
+				? velInstrumentToEarth($d,$i,
+					velBeamToInstrument($d,
+						@{$d->{ENSEMBLE}[$i]->{BT_VELOCITY}}))
+				: velApplyHdgBias($d,$i,@{$d->{ENSEMBLE}[$i]->{BT_VELOCITY}});
+		next unless (abs($BT[3]) < 0.05);
+		$d->{ENSEMBLE}[$i]->{DEPTH_BT} =
+		$d->{ENSEMBLE}[$i]->{DEPTH_BT} =
+			 $d->{ENSEMBLE}[$i]->{BT_RANGE}[0]/4 +
+			 $d->{ENSEMBLE}[$i]->{BT_RANGE}[1]/4 +
+ 			 $d->{ENSEMBLE}[$i]->{BT_RANGE}[2]/4 +
+			 $d->{ENSEMBLE}[$i]->{BT_RANGE}[3]/4;
+		$d->{ENSEMBLE}[$i]->{DEPTH_BT} *= -1
+			if ($d->{ENSEMBLE}[$i]->{XDUCER_FACING_UP});
+		$d->{ENSEMBLE}[$i]->{DEPTH_BT} += $d->{ENSEMBLE}[$i]->{DEPTH};
+		$guesses[int($d->{ENSEMBLE}[$i]->{DEPTH_BT})+$z_offset]++;
+		$nd++;
+	}
+	return undef unless ($nd>5);
+
+	my($mode,$nmax);
+	for ($i=0; $i<=$#guesses; $i++) {			# find mode
+		$nmax=$guesses[$i],$mode=$i-$z_offset
+			if ($guesses[$i] > $nmax);
+	}
+
+	$nd = 0;
+	for ($i=$be-$search_width; $i<=$be+$search_width; $i++) {
+		next unless defined($d->{ENSEMBLE}[$i]->{DEPTH_BT});
+		if (abs($d->{ENSEMBLE}[$i]->{DEPTH_BT}-$mode) <= $mode_width) {
+			$dd += $d->{ENSEMBLE}[$i]->{DEPTH_BT};
+			$nd++;
+		} else {
+			$d->{ENSEMBLE}[$i]->{DEPTH_BT} = undef;
+		}
+	}
+	return undef unless ($nd >= 2);
+
+	$dd /= $nd;
+	for ($i=$be-$search_width; $i<=$be+$search_width; $i++) {
+		next unless defined($d->{ENSEMBLE}[$i]->{DEPTH_BT});
+		$sd += ($d->{ENSEMBLE}[$i]->{DEPTH_BT}-$dd)**2;
+	}
+
+	return ($dd, sqrt($sd/($nd-1)));
+}
+
+#======================================================================
+# c = soundSpeed()
+#======================================================================
+
+# Taken from the RDI BroadBand primer manual. The reference given there
+# is Urick (1983).
+
+sub soundSpeed($$$)
+{
+	my($salin,$temp,$depth) = @_;
+	return 1449.2 + 4.6*$temp -0.055*$temp**2  + 0.00029*$temp**3 +
+				(1.34 - 0.01*$temp) * ($salin - 35) + 0.016*$depth;
+}
+
+1;