Merge pull request GliderToolsCommunity#39 from dhruvbalwada/add_spice

fixed spice calculations

glidertools/physics.py

@@ -208,3 +208,51 @@ def pad_nan(a):
         )
 
         return n2
+
+
+    # compute spice 
+    def spice0(salt_PSU, temp_C, pres_db, lat, lon):
+        """
+        Calculate spiciness from glider measurements of salinity and temperature.
+
+        Parameters
+        ----------
+        salt_PSU : array, dtype=float, shape=[n, ]
+            practical salinty
+        temp_C : array, dtype=float, shape=[n, ]
+        temperature in deg C
+        pres_db : array, dtype=float, shape=[n, ]
+            pressure in decibar
+        lat : array, dtype=float, shape=[n, ]
+            latitude in degrees north
+        lon : array, dtype=float, shape=[n, ]
+            longitude in degrees east
+
+        Returns
+        -------
+        potential_density : array, dtype=float, shape=[n, ]
+
+
+        Note
+        ----
+        Using seawater.dens does not yield the same results as this function. We
+        get very close results to what the SeaGlider Basestation returns with this
+        function. The difference of this function with the basestation is on
+        average ~ 0.003 kg/m3
+        """
+        import gsw
+        salt_abs = gsw.SA_from_SP(salt_PSU, pres_db, lon, lat)
+        cons_temp = gsw.CT_from_t(salt_abs, temp_C, pres_db)
+
+        spice0 = gsw.spiciness0(salt_abs, cons_temp)
+
+        spice0 = transfer_nc_attrs(
+            getframe(),
+            temp_C,
+            spice0,
+            'spiciness0',
+            units=' ',
+            comment='',
+            standard_name='spiciness0',
+        )
+        return spice0