diff --git a/nansat/mosaic.py b/nansat/mosaic.py
index cd1077407..135942c28 100644
--- a/nansat/mosaic.py
+++ b/nansat/mosaic.py
@@ -89,20 +89,22 @@ class Layer:
     def __init__(self, fileName, bands=[1],
                         opener=Nansat, maskName='mask',
                         doReproject=True, eResampleAlg=0,
-                        period=(None,None)):
-        ''' Set parameters of processing '''
+                        period=(None,None),
+                        logLevel=30):
+        # Set parameters of processing
         self.fileName     = fileName
         self.bands        = bands
         self.opener       = opener
         self.maskName     = maskName
         self.doReproject  = doReproject
         self.period       = period
-        self.n            = None
         self.eResampleAlg = eResampleAlg
+        self.logLevel     = logLevel
 
-    def make_nansat_object(self, domain=None):
-        ''' Open self.fileName with self.opener '''
-        self.n = self.opener(self.fileName)
+    def make_nansat_object(self, domain):
+        # Open self.fileName with self.opener
+        print 'Layer', self.fileName, self.logLevel
+        self.n = self.opener(self.fileName, logLevel=self.logLevel)
         if self.doReproject:
             self.n.reproject(domain, eResampleAlg=self.eResampleAlg)
 
@@ -133,29 +135,6 @@ def get_mask_array(self):
         return mask
 
 
-
-"""
-
-    def _get_layer_image(self):
-        '''Get nansat object from the specifed file
-
-        Open file with Nansat
-        Return, if it is within a given period,
-
-        Returns:
-        --------
-            Nansat object or None
-        '''
-        # open file using Nansat or its child class
-        n = self.nClass(self.fileName, logLevel=self.logger.level)
-
-        # check if image is out of period
-        self.logger.info('Try to get time from %s' % f)
-        if n is not None:
-
-        return n
-"""
-
 class Mosaic(Nansat):
     '''Container for mosaicing methods
 
@@ -215,17 +194,18 @@ def average(self, files=[], bands=[1], doReproject=True, maskName='mask',
             self.logger.error('No input files given!')
             return
 
-        # create list of layers
-        domain = Nansat(domain=self)
-        layers = [Layer(ifile, bands, opener, maskName, doReproject,
-                        eResampleAlg, period) for ifile in files]
-
         # get desired shape
         dstShape = self.shape()
-
         # preallocate shared mem array
         sharedArray = mp.Array(ctypes.c_float, [0]*(2+len(bands)+len(bands)) * dstShape[0] * dstShape[1])
 
+        # create list of layers
+        domain = Nansat(domain=self)
+        layers = [Layer(ifile, bands, opener, maskName, doReproject,
+                        eResampleAlg, period, self.logger.level)
+                        for ifile in files]
+
+        # test in debug
         #sumup(layers[0])
 
         # prepare pool of processors
@@ -244,6 +224,13 @@ def average(self, files=[], bands=[1], doReproject=True, maskName='mask',
                                      (2+len(bands)*2, dstShape[0], dstShape[1]),
                                      'float32')
 
+        # cleanup
+        pool.terminate()
+        pool = None
+        layers = None
+        metadata = None
+        sharedArray = None
+
         cntMat = sharedNDArray[0]
         maskMat = sharedNDArray[1]
         avgMat = sharedNDArray[2:2+len(bands)]
@@ -281,7 +268,9 @@ def average(self, files=[], bands=[1], doReproject=True, maskName='mask',
 
     def _get_cube(self, files, band, doReproject, maskName, opener,
                                                     eResampleAlg,
-                                                    period):
+                                                    period,
+                                                    vmin=-np.inf,
+                                                    vmax=np.inf):
         '''Make cube with data from one band of input files
 
         Open files, reproject, get band, insert into cube
@@ -317,17 +306,23 @@ def _get_cube(self, files, band, doReproject, maskName, opener,
         # for all input files
         for i, f in enumerate(files):
             self.logger.info('Processing %s' % f)
-            layer = Layer(f, [band], opener, maskName, doReproject, eResampleAlg, period)
-
+            layer = Layer(f, [band], opener, maskName, doReproject,
+                            eResampleAlg, period, logLevel=self.logger.level)
             # get nansat from the input Layer
             layer.make_nansat_object(domain)
+
             # if not in the period, quit
             if not layer.within_period():
                 continue
             # get mask
             mask = layer.get_mask_array()
             # get arrays with data
-            bandArray = layer.n[band]
+            bandArray = layer.n[band].astype('float32')
+            # remove invalid data
+            bandArray[mask < 64] = np.nan
+            bandArray[bandArray < vmin] = np.nan
+            bandArray[bandArray > vmax] = np.nan
+
             # get metadata
             bandMetadata = layer.n.get_metadata(bandID=band)
 
@@ -341,7 +336,8 @@ def _get_cube(self, files, band, doReproject, maskName, opener,
         return dataCube, maskMat.max(0), bandMetadata
 
     def median(self, files=[], bands=[1], doReproject=True, maskName='mask',
-                opener=Nansat, threads=1, eResampleAlg=0, period=(None,None)):
+                opener=Nansat, eResampleAlg=0, period=(None,None),
+                vmin=-np.inf, vmax=np.inf):
         '''Calculate median of input bands
 
         Memory and CPU greedy method. Generates 3D cube from bands of
@@ -378,7 +374,7 @@ def median(self, files=[], bands=[1], doReproject=True, maskName='mask',
                                                     maskName,
                                                     opener,
                                                     eResampleAlg,
-                                                    period)
+                                                    period, vmin, vmax)
             median = st.nanmedian(cube, axis=0)
 
             # add band and std with metadata
diff --git a/nansat/nansat.py b/nansat/nansat.py
index 36c63c06d..d3874b038 100644
--- a/nansat/nansat.py
+++ b/nansat/nansat.py
@@ -1727,6 +1727,7 @@ def _get_mapper(self, mapperName, **kwargs):
                 tmpVRT._create_band({'SourceFilename': self.fileName,
                                      'SourceBand': iBand + 1})
                 tmpVRT.dataset.FlushCache()
+            self.mapper = 'gdal_bands'
 
         # if GDAL cannot open the file, and no mappers exist which can make VRT
         if tmpVRT is None and gdalDataset is None: