diff --git a/src/imars3d/backend/dataio/data.py b/src/imars3d/backend/dataio/data.py
index 5b92cbdf..787ff5f3 100644
--- a/src/imars3d/backend/dataio/data.py
+++ b/src/imars3d/backend/dataio/data.py
@@ -104,14 +104,14 @@ class load_data(param.ParameterizedFunction):
 
     Notes
     -----
-        There are two main signatures to load the data:
+        There are three main signatures to load the data:
         1. load_data(ct_files=ctfs, ob_files=obfs, dc_files=dcfs)
         2. load_data(ct_dir=ctdir, ob_dir=obdir, dc_dir=dcdir)
+        3. load_data(ct_dir=ctdir, ob_files=obfs, dc_files=dcfs)
 
-        The two signatures are mutually exclusive, and dc_files and dc_dir are optional
-        in both cases as some experiments do not have dark current measurements.
+        In all signatures dc_files and dc_dir are optional
 
-        The fnmatch selectors are applicable in both signature, which help to down-select
+        The fnmatch selectors are applicable in all signature, which help to down-select
         files if needed. Default is set to "*", which selects everything.
         Also, if ob_fnmatch and dc_fnmatch are set to "None" in the second signature call, the
         data loader will attempt to read the metadata embedded in the first ct file to find obs
@@ -157,9 +157,43 @@ def __call__(self, **params):
         #    use set to simplify call signature checking
         sigs = set([k.split("_")[-1] for k in params.keys() if "fnmatch" not in k])
         ref = {"files", "dir"}
-        if sigs.intersection(ref) == {"files", "dir"}:
-            logger.error("Files and dir cannot be used at the same time")
-            raise ValueError("Mix usage of allowed signature.")
+
+        if ("ct_dir" in params.keys()) and ("ob_files" in params.keys()):
+            logger.debug("Load ct by directory, ob and dc (if any) by files")
+            ct_dir = params.get("ct_dir")
+            if not Path(ct_dir).exists():
+                logger.error(f"ct_dir {ct_dir} does not exist.")
+                raise ValueError("ct_dir does not exist.")
+            else:
+                ct_dir = Path(ct_dir)
+
+            # gather the ct_files
+            ct_fnmatch = params.get("ct_fnmatch", "*")
+            ct_files = ct_dir.glob(ct_fnmatch)
+            ct_files = list(map(str, ct_files))
+            ct_files.sort()
+
+            ob_files = (params.get("ob_files"),)
+            dc_files = (params.get("dc_files", []),)  # it is okay to skip dc
+
+            ob_files = ob_files[0]
+            dc_files = dc_files[0]
+
+            ct, ob, dc = _load_by_file_list(
+                ct_files=ct_files,
+                ob_files=ob_files,
+                dc_files=dc_files,  # it is okay to skip dc
+                ct_fnmatch=params.get("ct_fnmatch", "*"),  # incase None got leaked here
+                ob_fnmatch=params.get("ob_fnmatch", "*"),
+                dc_fnmatch=params.get("dc_fnmatch", "*"),
+                max_workers=self.max_workers,
+                tqdm_class=params.tqdm_class,
+            )
+
+        elif ("ct_files" in params.keys()) and ("ob_dir" in params.keys()):
+            logger.error("ct_files and ob_dir mixed not allowed!")
+            raise ValueError("Mix signatures (ct_files, ob_dir) not allowed!")
+
         elif sigs.intersection(ref) == {"files"}:
             logger.debug("Load by file list")
             ct, ob, dc = _load_by_file_list(
diff --git a/tests/unit/backend/dataio/test_data.py b/tests/unit/backend/dataio/test_data.py
index af912989..82cb87b0 100644
--- a/tests/unit/backend/dataio/test_data.py
+++ b/tests/unit/backend/dataio/test_data.py
@@ -97,6 +97,8 @@ def test_load_data(
     # error_0: incorrect input argument types
     with pytest.raises(ValueError):
         load_data(ct_files=1, ob_files=[], dc_files=[])
+        load_data(ct_dir=1, ob_files=[])
+        load_data(ct_files=[], ob_dir="/tmp")
         load_data(ct_files=[], ob_files=[], dc_files=[], ct_fnmatch=1)
         load_data(ct_files=[], ob_files=[], dc_files=[], ob_fnmatch=1)
         load_data(ct_files=[], ob_files=[], dc_files=[], dc_fnmatch=1)
@@ -106,16 +108,16 @@ def test_load_data(
     # error_1: out of bounds value
     with pytest.raises(ValueError):
         load_data(ct_files=[], ob_files=[], dc_files=[], max_workers=-1)
-    # error_2: mix usage of function signature 1 and 2
-    with pytest.raises(ValueError):
-        load_data(ct_files=[], ob_files=[], dc_files=[], ct_dir="/tmp", ob_dir="/tmp")
     # error_3: no valid signature found
     with pytest.raises(ValueError):
         load_data(ct_fnmatch=1)
-    # case_0: load data from file list
+    # case_0: load ct from directory, ob and dc from files
+    rst = load_data(ct_dir="/tmp", ob_files=["3", "4"], dc_files=["5", "6"])
+    np.testing.assert_almost_equal(np.array(rst).flatten(), np.arange(1, 5, dtype=float))
+    # case_1: load data from file list
     rst = load_data(ct_files=["1", "2"], ob_files=["3", "4"], dc_files=["5", "6"])
     np.testing.assert_almost_equal(np.array(rst).flatten(), np.arange(1, 5, dtype=float))
-    # case_1: load data from given directory
+    # case_2: load data from given directory
     rst = load_data(ct_dir="/tmp", ob_dir="/tmp", dc_dir="/tmp")
     np.testing.assert_almost_equal(np.array(rst).flatten(), np.arange(1, 5, dtype=float))