Merge 50eebbc into 1e4a4a1

Makefile

@@ -76,6 +76,7 @@ clean:
 	rm -rvf logo.png cookbook/logo.png
 	rm -rvf crust2.tar.gz cookbook/crust2.tar.gz
 	rm -rvf bouguer_alps_egm08.grd cookbook/bouguer_alps_egm08.grd
+	rm -rvf *.gdf cookbook/*.gdf
 
 clean-docs:
 	cd doc; make clean

cookbook/gravmag_normal_gravity.py

@@ -0,0 +1,49 @@
+"""
+GravMag: Calculate the gravity disturbance and Bouguer anomaly for Hawaii
+"""
+from fatiando.gravmag import normal_gravity
+from fatiando.vis import mpl
+import numpy as np
+import urllib
+
+# Download the gravity and topography data
+url = 'https://raw.githubusercontent.com/leouieda/geofisica1/master/data/'
+urllib.urlretrieve(url + 'eigen-6c3stat-havai.gdf',
+                   filename='eigen-6c3stat-havai.gdf')
+urllib.urlretrieve(url + 'etopo1-havai.gdf',
+                   filename='etopo1-havai.gdf')
+# Load them with numpy
+lon, lat, height, gravity = np.loadtxt('eigen-6c3stat-havai.gdf', skiprows=34,
+                                       unpack=True)
+topo = np.loadtxt('etopo1-havai.gdf', skiprows=30, usecols=[-1], unpack=True)
+shape = (151, 151)
+area = (lon.min(), lon.max(), lat.min(), lat.max())
+
+# First, lets calculate the gravity disturbance (e.g., the free-air anomaly)
+# We'll do this using the closed form of the normal gravity for the WGS84
+# ellipsoid
+gamma = normal_gravity.gamma_closed_form(lat, height)
+disturbance = gravity - gamma
+
+# Now we can remove the effect of the Bouguer plate to obtain the Bouguer
+# anomaly. We'll use the standard densities of 2.67 g.cm^-3 for crust and 1.04
+# g.cm^-3 for water.
+bouguer = disturbance - normal_gravity.bouguer_plate(topo)
+
+mpl.figure(figsize=(14, 3.5))
+bm = mpl.basemap(area, projection='merc')
+mpl.subplot(131)
+mpl.title('Gravity (mGal)')
+mpl.contourf(lon, lat, gravity, shape, 60, cmap=mpl.cm.Reds, basemap=bm)
+mpl.colorbar(pad=0)
+mpl.subplot(132)
+mpl.title('Gravity disturbance (mGal)')
+amp = np.abs(disturbance).max()
+mpl.contourf(lon, lat, disturbance, shape, 60, cmap=mpl.cm.RdBu_r, basemap=bm,
+             vmin=-amp, vmax=amp)
+mpl.colorbar(pad=0)
+mpl.subplot(133)
+mpl.title('Bouguer anomaly (mGal)')
+mpl.contourf(lon, lat, bouguer, shape, 60, cmap=mpl.cm.Reds, basemap=bm)
+mpl.colorbar(pad=0)
+mpl.show()

doc/api/gravmag.normal_gravity.rst

@@ -0,0 +1,9 @@
+.. _fatiando_gravmag_normal_gravity:
+
+Compute normal gravity and reductions (``fatiando.gravmag.normal_gravity``)
+===========================================================================
+
+
+.. automodule:: fatiando.gravmag.normal_gravity
+   :members:
+   :show-inheritance:

doc/api/gravmag.rst

@@ -24,3 +24,4 @@ Gravity and magnetics (``fatiando.gravmag``)
     gravmag.transform.rst
     gravmag.half_sph_shell.rst
     gravmag.magdir.rst
+    gravmag.normal_gravity.rst

doc/changelog.rst

@@ -10,6 +10,10 @@ Version (future)
 
 **Changes**:
 
+* **New module** :ref:`fatiando.gravmag.normal_gravity
+  <fatiando_gravmag_normal_gravity>` to calculate normal gravity (the gravity
+  of reference ellipsoids).
+  (`PR 133 <https://github.com/fatiando/fatiando/pull/133>`_)
 * Using `versioneer <https://github.com/warner/python-versioneer>`__ to manage
   version numbers. Access the version number + git commit hash from
   ``fatiando.__version__``.

fatiando/gravmag/__init__.py

@@ -37,6 +37,8 @@
 The processing modules offer tools to prepare potential field data before or
 after modeling.
 
+* :mod:`~fatiando.gravmag.normal_gravity`: Compute normal gravity and
+  reductions.
 * :mod:`~fatiando.gravmag.eqlayer`: Equivalent layer processing
 * :mod:`~fatiando.gravmag.transform`: Space domain potential field
   transformations, like upward continuation