Add NISAR loading and auxiliary stack support

src/mintpy/cli/prep_nisar.py

@@ -49,6 +49,15 @@ def create_parser(subparsers=None):
         help="path to the mask (default: %(default)s).",
     )
 
+    parser.add_argument(
+        "-freq",
+        "--frequency",
+        dest="frequency",
+        choices=["auto", "A", "B"],
+        default="auto",
+        help="NISAR frequency to load: auto defaults to A (default: %(default)s).",
+    )
+
     parser.add_argument(
         "-o",
         "--out-dir",

src/mintpy/defaults/smallbaselineApp.cfg

@@ -30,6 +30,7 @@ mintpy.load.processor       = auto  #[isce, aria, hyp3, gmtsar, snap, gamma, roi
 mintpy.load.autoPath        = auto  #[yes / no], auto for no, use pre-defined auto path
 mintpy.load.updateMode      = auto  #[yes / no], auto for yes, skip re-loading if HDF5 files are complete
 mintpy.load.compression     = auto  #[gzip / lzf / none / default], auto for default (none/lzf for stack/geometry).
+mintpy.load.frequency       = auto  #[auto / A / B], auto for A, NISAR only
 ##---------for ISCE only:
 mintpy.load.metaFile        = auto  #[path of common metadata file for the stack], i.e.: ./reference/IW1.xml, ./referenceShelve/data.dat
 mintpy.load.baselineDir     = auto  #[path of the baseline dir], i.e.: ./baselines

src/mintpy/load_data.py

@@ -636,11 +636,28 @@ def prepare_metadata(iDict):
         dem_file = iDict['mintpy.load.demFile']
         gunw_files = iDict['mintpy.load.unwFile']
         water_mask = iDict['mintpy.load.waterMaskFile']
+        frequency = iDict.get('mintpy.load.frequency', 'auto')
+
+        if str(dem_file).lower() in ['auto', 'none', 'no', '']:
+            raise ValueError(
+                'mintpy.load.demFile is required for processor=nisar. '
+                'Please set it to a real DEM path in the template.'
+            )
+        dem_file = os.path.expanduser(str(dem_file))
+        if not os.path.isfile(dem_file):
+            raise FileNotFoundError(
+                f'No DEM file found for mintpy.load.demFile: {dem_file}'
+            )
+
+        if len(glob.glob(str(gunw_files))) == 0:
+            raise FileNotFoundError(
+                f'No input GUNW files found for mintpy.load.unwFile: {gunw_files}'
+            )
 
         # run prep_*.py
-        iargs = ['-i', gunw_files, '-d', dem_file]
+        iargs = ['-i', gunw_files, '-d', dem_file, '--frequency', frequency]
 
-        if os.path.exists(water_mask):
+        if str(water_mask).lower() not in ['auto', 'none', 'no', ''] and os.path.exists(water_mask):
             iargs = iargs + ['--mask', water_mask]
 
         if iDict['mintpy.subset.yx']: