diff --git a/imap_processing/ultra/constants.py b/imap_processing/ultra/constants.py
index e95549a31..2bfa66ebf 100644
--- a/imap_processing/ultra/constants.py
+++ b/imap_processing/ultra/constants.py
@@ -160,3 +160,7 @@ class UltraConstants:
     # For FOV calculations
     FOV_THETA_OFFSET_DEG = 0.0
     FOV_PHI_LIMIT_DEG = 60.0
+
+    # For spatiotemporal culling
+    EARTH_RADIUS_KM: float = 6378.1
+    DEFAULT_EARTH_CULLING_RADIUS = EARTH_RADIUS_KM * 30
diff --git a/imap_processing/ultra/l1c/helio_pset.py b/imap_processing/ultra/l1c/helio_pset.py
index 13add46f8..fc9f76ef5 100644
--- a/imap_processing/ultra/l1c/helio_pset.py
+++ b/imap_processing/ultra/l1c/helio_pset.py
@@ -13,6 +13,7 @@
     met_to_ttj2000ns,
     ttj2000ns_to_et,
 )
+from imap_processing.ultra.constants import UltraConstants
 from imap_processing.ultra.l1b.ultra_l1b_culling import get_de_rejection_mask
 from imap_processing.ultra.l1c.l1c_lookup_utils import (
     build_energy_bins,
@@ -203,7 +204,7 @@ def calculate_helio_pset(
     # Compute mask for culling the Earth
     compute_culling_mask(
         time_bins,
-        6378.1,  # Earth radius
+        UltraConstants.DEFAULT_EARTH_CULLING_RADIUS,
         helio_pset_quality_flags,
         nside=nside,
     )
@@ -229,8 +230,10 @@ def calculate_helio_pset(
     pset_dict["spin_phase_step"] = np.arange(len(deadtime_ratios))
     pset_dict["quality_flags"] = helio_pset_quality_flags[np.newaxis, ...]
 
-    pset_dict["scatter_theta"] = scattering_theta
-    pset_dict["scatter_phi"] = scattering_phi
+    # Convert FWHM to gaussian uncertainty by dividing by 2.355
+    # See algorithm documentation (section 3.5.7, third bullet point) for more details
+    pset_dict["scatter_theta"] = scattering_theta / 2.355
+    pset_dict["scatter_phi"] = scattering_phi / 2.355
     pset_dict["scatter_threshold"] = scattering_thresholds
 
     # Add the energy delta plus/minus to the dataset
diff --git a/imap_processing/ultra/l1c/spacecraft_pset.py b/imap_processing/ultra/l1c/spacecraft_pset.py
index f04e6d033..d9b898357 100644
--- a/imap_processing/ultra/l1c/spacecraft_pset.py
+++ b/imap_processing/ultra/l1c/spacecraft_pset.py
@@ -13,6 +13,7 @@
     met_to_ttj2000ns,
     ttj2000ns_to_et,
 )
+from imap_processing.ultra.constants import UltraConstants
 from imap_processing.ultra.l1b.ultra_l1b_culling import get_de_rejection_mask
 from imap_processing.ultra.l1c.l1c_lookup_utils import (
     build_energy_bins,
@@ -190,7 +191,7 @@ def calculate_spacecraft_pset(
     # Compute mask for culling the Earth
     compute_culling_mask(
         time_bins,
-        6378.1,  # Earth radius
+        UltraConstants.DEFAULT_EARTH_CULLING_RADIUS,
         spacecraft_pset_quality_flags,
         nside=nside,
     )