JP-3237 Compute correct exposure times for combined images

CHANGES.rst

@@ -70,6 +70,9 @@ resample
   image shape and the bounding box both for ``SCI`` image as well as for the
   ``ERR`` and ``VARIANCE_*`` images. [#7774]
 
+- Update the following exposure time keywords: XPOSURE (EFFEXPTM),
+  DURATION and TELAPSE. [#7793]
+
 residual_fringe
 ---------------
 

jwst/resample/resample.py

@@ -363,17 +363,27 @@ def update_exposure_times(self, output_model):
         """Modify exposure time metadata in-place"""
         total_exposure_time = 0.
         exposure_times = {'start': [], 'end': []}
+        duration = 0.0
         for exposure in self.input_models.models_grouped:
             total_exposure_time += exposure[0].meta.exposure.exposure_time
             exposure_times['start'].append(exposure[0].meta.exposure.start_time)
             exposure_times['end'].append(exposure[0].meta.exposure.end_time)
+            duration += exposure[0].meta.exposure.duration
 
         # Update some basic exposure time values based on output_model
         output_model.meta.exposure.exposure_time = total_exposure_time
         output_model.meta.exposure.start_time = min(exposure_times['start'])
         output_model.meta.exposure.end_time = max(exposure_times['end'])
         output_model.meta.resample.product_exposure_time = total_exposure_time
 
+        # Update other exposure time keywords:
+        # XPOSURE (identical to the total effective exposure time, EFFEXPTM)
+        xposure = total_exposure_time
+        output_model.meta.exposure.effective_exposure_time = xposure
+        # DURATION (identical to TELAPSE, elapsed time)
+        output_model.meta.exposure.duration = duration
+        output_model.meta.exposure.elapsed_exposure_time = duration
+
     @staticmethod
     def drizzle_arrays(insci, inwht, input_wcs, output_wcs, outsci, outwht,
                        outcon, uniqid=1, xmin=0, xmax=0, ymin=0, ymax=0,