diff --git a/xrspatial/reproject/__init__.py b/xrspatial/reproject/__init__.py
index ac9f93cd..33292f81 100644
--- a/xrspatial/reproject/__init__.py
+++ b/xrspatial/reproject/__init__.py
@@ -14,6 +14,8 @@
 import numpy as np
 import xarray as xr
 
+from xrspatial.utils import _validate_raster
+
 from ._crs_utils import _detect_nodata, _detect_source_crs, _resolve_crs
 from ._grid import (
     _chunk_bounds,
@@ -522,11 +524,8 @@ def reproject(
         If vertical transformation was applied, ``attrs['vertical_crs']``
         records the target vertical datum.
     """
-    if not isinstance(raster, xr.DataArray):
-        raise TypeError(
-            f"reproject(): raster must be an xr.DataArray, "
-            f"got {type(raster).__name__}"
-        )
+    _validate_raster(raster, func_name='reproject', name='raster',
+                     ndim=(2, 3))
 
     _validate_grid_params(
         resolution=resolution,
@@ -1360,6 +1359,10 @@ def merge(
     if not rasters:
         raise ValueError("merge(): rasters list must not be empty")
 
+    for i, r in enumerate(rasters):
+        _validate_raster(r, func_name='merge', name=f'rasters[{i}]',
+                         ndim=(2, 3))
+
     _validate_grid_params(
         resolution=resolution,
         bounds=bounds,
diff --git a/xrspatial/reproject/_vertical.py b/xrspatial/reproject/_vertical.py
index e0013e54..430cea53 100644
--- a/xrspatial/reproject/_vertical.py
+++ b/xrspatial/reproject/_vertical.py
@@ -239,6 +239,11 @@ def geoid_height_raster(raster, model='EGM96'):
     """
     import xarray as xr
 
+    from xrspatial.utils import _validate_raster
+
+    _validate_raster(raster, func_name='geoid_height_raster',
+                     name='raster', ndim=(2, 3))
+
     data, left, top, res_x, res_y, h, w = _load_geoid(model)
 
     y = raster.coords[raster.dims[-2]].values.astype(np.float64)
diff --git a/xrspatial/tests/test_reproject.py b/xrspatial/tests/test_reproject.py
index 704469c4..9fbd268c 100644
--- a/xrspatial/tests/test_reproject.py
+++ b/xrspatial/tests/test_reproject.py
@@ -507,7 +507,7 @@ def test_missing_crs_raises(self):
 
     def test_non_dataarray_raises(self):
         from xrspatial.reproject import reproject
-        with pytest.raises(TypeError, match="xr.DataArray"):
+        with pytest.raises(TypeError, match="xarray.DataArray"):
             reproject(np.zeros((4, 4)), 'EPSG:4326')
 
     def test_output_has_crs_attr(self):
@@ -1519,6 +1519,51 @@ def test_numpy_chunk_source_window_guard(self):
         assert result.shape[0] > 0 and result.shape[1] > 0
 
 
+# =====================================================================
+# Issue #1431: _validate_raster on public API inputs
+# =====================================================================
+
+class TestValidateRasterInputs:
+    """reproject(), merge(), geoid_height_raster() validate inputs (#1431)."""
+
+    def test_reproject_rejects_1d_dataarray(self):
+        from xrspatial.reproject import reproject
+        bad = xr.DataArray(np.zeros(5, dtype=np.float64), dims=('y',))
+        with pytest.raises(ValueError, match=r"must be 2D ?or 3D"):
+            reproject(bad, 'EPSG:4326')
+
+    def test_reproject_rejects_complex_dtype(self):
+        from xrspatial.reproject import reproject
+        bad = xr.DataArray(
+            np.zeros((4, 4), dtype=np.complex128),
+            dims=('y', 'x'),
+            coords={'y': np.arange(4), 'x': np.arange(4)},
+        )
+        with pytest.raises(ValueError, match="real numeric"):
+            reproject(bad, 'EPSG:4326')
+
+    def test_merge_rejects_non_dataarray_element(self):
+        from xrspatial.reproject import merge
+        good = xr.DataArray(
+            np.zeros((4, 4), dtype=np.float64),
+            dims=('y', 'x'),
+            coords={'y': np.arange(4), 'x': np.arange(4)},
+        )
+        with pytest.raises(TypeError, match="xarray.DataArray"):
+            merge([good, np.zeros((4, 4))])
+
+    def test_geoid_height_raster_rejects_non_dataarray(self):
+        from xrspatial.reproject import geoid_height_raster
+        with pytest.raises(TypeError, match="xarray.DataArray"):
+            geoid_height_raster(np.zeros((4, 4)))
+
+    def test_geoid_height_raster_rejects_1d_dataarray(self):
+        from xrspatial.reproject import geoid_height_raster
+        bad = xr.DataArray(np.zeros(5, dtype=np.float64), dims=('y',))
+        with pytest.raises(ValueError, match=r"must be 2D ?or 3D"):
+            geoid_height_raster(bad)
+
+
 # =====================================================================
 # Issue #1433: grid/bounds/precision parameter validation
 # =====================================================================