diff --git a/README.md b/README.md
index e178c1a..768f652 100644
--- a/README.md
+++ b/README.md
@@ -111,13 +111,13 @@ station_obs_file : <path>/pollen_measured_2024020118.atab
 station_mod_file : <path>/pollen_modelled_2024020118.atab
 hour_incr : 1
 ```
-`pov_infile`: This GRIB2 file must include the fields `tthrs`, `tthre` (for POAC, `saisl` instead), `saisn` and `ctsum` if the module `update_phenology` is called. If the module `update_strength` is called `pov_infile` must include the fields `saisn` and `tune`. `pov_infile` is used as template for `pov_outfile`, i.e. the whole file is copied to `pov_outfile` with adapted values. Date and time information of `pov_infile` does not have to be correct, ICON just throws warnings.
+`pov_infile`: This GRIB2 file must include the fields `tthrs`, `tthre` (for POAC, `saisl` instead), `saisn` and `ctsum` if the module `update_phenology` is called. If the module `update_strength` is called `pov_infile` must include the fields `saisn` and `tune`. If at least one of these mandatory fields is missing the package exits with status 1 and tells the user. `pov_infile` is used as template for `pov_outfile`, i.e. the whole file is copied to `pov_outfile` with adapted values. Date and time information of `pov_infile` does not have to be correct, ICON just throws warnings.
 
 `pov_outfile`: Same as `pov_infile` but with adapted values.
 `t2m_file`: This GRIB2 file must include T_2M valid for 12h UTC of the current day (only used if the module `update_phenology` is called).
 `const_file`: This GRIB2 file must contain CLON and CLAT of the unstructured grid used in `pov_infile` and `t2m_file`.
-`station_obs_file`: Observed hourly pollen concentrations (ATAB format) of the latest 120 hours relative to the target date of `pov_outfile`. The timestamps of the data in this file may vary depending on data availability, time of extraction etc. Missing values are allowed.
-`station_mod_file`: Modelled hourly pollen concentrations (ATAB format) of the latest 120 hours relative to the target date of `pov_outfile`. The timestamps of the data in this file may vary depending on data availability, time of extraction etc. Missing values are allowed. Same stations as in `station_obs_file` (only used if the module `update_strength` is called).
+`station_obs_file`: Observed hourly pollen concentrations (ATAB format) of the latest 120 hours relative to the target date of `pov_outfile`. The timestamps of the data in this file may vary depending on data availability, time of extraction etc. Missing values are allowed but at least 50% of each station must be there. If not, the package exits with status 1 and tells the user.
+`station_mod_file`: Modelled hourly pollen concentrations (ATAB format) of the latest 120 hours relative to the target date of `pov_outfile`. The timestamps of the data in this file may vary depending on data availability, time of extraction etc. In case of missing values the package exits with status 1 and tells the user. Same stations as in `station_obs_file` (only used if the module `update_strength` is called).
 `hour_incr`: Increment of the timestamp of the outfile relative to the infile in hours (defaults to 1; negative values also supported). This parameter should be adapted if the calibration is done for a subsequent run more than one hour ahead.
 
 
diff --git a/src/realtime_pollen_calibration/update_phenology.py b/src/realtime_pollen_calibration/update_phenology.py
index f9a1c88..c2cfe55 100644
--- a/src/realtime_pollen_calibration/update_phenology.py
+++ b/src/realtime_pollen_calibration/update_phenology.py
@@ -7,6 +7,7 @@
 """A module for the update of start and end of the pollen season."""
 
 # Standard library
+import sys
 from datetime import datetime, timedelta
 
 import numpy as np
@@ -28,7 +29,6 @@ def read_pov_file(pov_infile, pol_fields):
     Args:
         pov_infile: GRIB2 file containing pollen fields.
         pol_fields: Names of the pollen fields.
-        config_obj: Object containing the configuration
 
     Returns:
         Fields for the pollen calibration.
@@ -51,6 +51,10 @@ def read_pov_file(pov_infile, pol_fields):
 
             # Delete the message
             codes_release(rec)
+
+    # Check if all mandatory fields for all species read are present. If not, exit.
+    utils.check_mandatory_fields(cal_fields, pol_fields, pov_infile)
+
     return cal_fields
 
 
@@ -80,10 +84,20 @@ def read_t2m_file(t2m_file, config_obj):
                 date_obj_fmt = date_obj.strftime("%Y-%m-%dT%H:00:00.000000000")
                 time_values = np.datetime64(date_obj_fmt)
             codes_release(rec)
+    if "T_2M" not in cal_fields:
+        print(
+            f"The mandatory field T_2M could not be read from {t2m_file}\n"
+            "No update of the phenology is done until this is fixed!\n"
+            "Pollen are still calculated but this should be fixed "
+            "within a few days."
+        )
+        sys.exit(1)
+    else:
+        print("T_2M field has been read from t2m_file.")
     return cal_fields, time_values
 
 
-def update_phenology_realtime(config_obj: utils.Config, verbose: bool = False):
+def update_phenology_realtime(config_obj: utils.Config, verbose: bool = True):
     """Update the temperature threshold fields and POACsaisl.
 
     Args:
diff --git a/src/realtime_pollen_calibration/update_strength.py b/src/realtime_pollen_calibration/update_strength.py
index 198adae..9dabded 100644
--- a/src/realtime_pollen_calibration/update_strength.py
+++ b/src/realtime_pollen_calibration/update_strength.py
@@ -61,10 +61,14 @@ def read_pov_file(pov_infile, pol_fields, config_obj):
                 time_values = np.datetime64(date_obj_fmt)
 
             codes_release(rec)
+
+    # Check if all mandatory fields for all species read are present. If not, exit.
+    utils.check_mandatory_fields(cal_fields, pol_fields, pov_infile)
+
     return cal_fields, time_values
 
 
-def update_strength_realtime(config_obj: utils.Config, verbose: bool = False):
+def update_strength_realtime(config_obj: utils.Config, verbose: bool = True):
     """Update the tune field.
 
     Args:
diff --git a/src/realtime_pollen_calibration/utils.py b/src/realtime_pollen_calibration/utils.py
index edca971..f0d4dd0 100644
--- a/src/realtime_pollen_calibration/utils.py
+++ b/src/realtime_pollen_calibration/utils.py
@@ -7,6 +7,7 @@
 """Utils for the command line tool."""
 # Standard library
 import logging
+import sys
 from collections import namedtuple
 from dataclasses import dataclass
 from datetime import datetime, timedelta
@@ -114,8 +115,9 @@ def read_clon_clat(const_file):
 
 
 def read_atab(
-    pollen_type: str, file_obs_stns: str, file_mod_stns: str = "", verbose: bool = False
+    pollen_type: str, file_obs_stns: str, file_mod_stns: str = "", verbose: bool = True
 ) -> ObsModData:
+    # pylint: disable=too-many-locals
     """Read the pollen concentrations and the station locations from the ATAB files.
 
     Args:
@@ -179,14 +181,17 @@ def read_obs_header(file_data: str):
     data = pd.read_csv(
         file_obs_stns,
         header=headerdata.n_header,
-        delim_whitespace=True,
+        sep=r"\s+",
         parse_dates=[[1, 2, 3, 4, 5]],
     )
     data = data[data["PARAMETER"] == pollen_type].iloc[:, 2:].to_numpy()
     if file_mod_stns != "":
         stn_indicators_mod = None
+        missing_value = None
         with open(file_mod_stns, encoding="utf-8") as f:
             for n, line in enumerate(f):
+                if line.strip()[0:18] == "Missing_value_code":
+                    missing_value = float(line.strip()[20:])
                 if line.strip()[0:9] == "Indicator":
                     stn_indicators_mod = np.array(line.strip()[29:].split("         "))
                 if line.strip()[0:9] == "PARAMETER":
@@ -196,14 +201,26 @@ def read_obs_header(file_data: str):
         data_mod = pd.read_csv(
             file_mod_stns,
             header=n_header_mod,
-            delim_whitespace=True,
+            sep=r"\s+",
             parse_dates=[[3, 4, 5, 6, 7]],
         )
         data_mod = data_mod[data_mod["PARAMETER"] == pollen_type].iloc[:, 4:].to_numpy()
+        if missing_value in data_mod:
+            print(
+                "There is at least one missing value",
+                f"in the model data file {file_mod_stns}.\n",
+                "Please check the reason (fieldextra retrieval namelist?).",
+                "No pollen calibration update is performed until this is fixed! ",
+                "Pollen in ICON will still work, but calibration fields get ",
+                "more and more outdated.",
+            )
+            sys.exit(1)
     else:
         data_mod = 0
         istation_mod = 0
-    data = treat_missing(data, headerdata.missing_value, verbose=verbose)
+    data = treat_missing(
+        data, headerdata.missing_value, headerdata.stn_indicators, verbose=verbose
+    )
     return ObsModData(
         data, headerdata.coord_stns, headerdata.missing_value, data_mod, istation_mod
     )
@@ -228,16 +245,14 @@ def create_data_arrays(cal_fields, clon, clat, time_values):
 def treat_missing(
     array,
     missing_value: float = -9999.0,
-    tune_pol_default: float = 1.0,
-    verbose: bool = False,
+    stn_indicators: str = "",
+    verbose: bool = True,
 ):
     """Treat the missing values of the input array.
 
     Args:
         array: Array containing the concentration values.
         missing_value: Value considered as a missing value.
-        tune_pol_default: Default value to which all values of a station
-                are set if more than 10% of the observations are missing.
         verbose: Optional additional debug prints.
 
     Returns:
@@ -251,27 +266,32 @@ def treat_missing(
         skip_missing_stn[istation] = np.count_nonzero(array_missing[:, istation])
         if verbose:
             print(
-                f"Station n°{istation} has",
+                f"Station {stn_indicators[istation]} has",
                 f"{skip_missing_stn[istation]} missing values",
             )
         if skip_missing_stn[istation] > 0:
             if (
                 np.count_nonzero(np.abs(array[:, istation] - missing_value) < 0.01)
                 / len(array[:, istation])
-                < 0.1
+                < 0.5
             ):
                 idx1 = np.where(np.abs(array[:, istation] - missing_value) > 0.01)
                 idx2 = np.where(np.abs(array[:, istation] - missing_value) < 0.01)
                 if verbose:
                     print(
-                        "Less than 10% of the data is missing, ",
+                        "Less than 50% of the data is missing, ",
                         f"mean of the rest is: {np.mean(array[idx1, istation])}",
                     )
                 array[idx2, istation] = np.mean(array[idx1, istation])
             else:
-                if verbose:
-                    print("More than 10% of the data is missing")
-                array[:, istation] = tune_pol_default
+                print(
+                    f"Station {stn_indicators[istation]} has more than 50% missing ",
+                    "data. Please check the reason (Does jretrievedwh still work?).\n",
+                    "No pollen calibration update is performed until this is fixed! ",
+                    "Pollen in ICON will still work, but calibration fields get ",
+                    "more and more outdated.",
+                )
+                sys.exit(1)
     return array
 
 
@@ -427,7 +447,6 @@ def get_change_tune(  # pylint: disable=R0913
                 f"Current tune value {tune_stns.values[0]} ",
                 f"and saisn: {saisn_stns.values[0]}",
             )
-            print("-----------------------------------------")
         if (saisn_stns > 0) and ((sum_obs <= 720) or (sum_mod <= 720)):
             if verbose:
                 print(
@@ -497,6 +516,7 @@ def get_change_phenol(  # pylint: disable=R0912,R0914,R0915
         sum_obs = np.sum(obs_mod_data.data_obs[:, istation])
         if verbose:
             print(
+                f"Current pollen type is: {pollen_type}, ",
                 f"Current station n°{istation}, ",
                 f"(lat: {obs_mod_data.coord_stns[istation][0]}, ",
                 f"lon: {obs_mod_data.coord_stns[istation][1]}), ",
@@ -615,6 +635,37 @@ def get_change_phenol(  # pylint: disable=R0912,R0914,R0915
     return ChangePhenologyFields(change_tthrs, change_tthre, change_saisl)
 
 
+def check_mandatory_fields(cal_fields, pol_fields, pov_infile):
+    """Check if all mandatory fields for all species read are present.
+
+    Args:
+        cal_fields: Dictionary of calibration fields.
+        pol_fields: Names of the pollen fields.
+        pov_infile: GRIB2 file containing pollen fields.
+
+    Exits:
+        If any mandatory fields are missing.
+
+    """
+    species_read = {key[:4] for key in cal_fields.keys()}
+
+    req_fields = [fld for fld in pol_fields if fld[:4] in species_read]
+
+    missing_fields = [fld for fld in req_fields if fld not in cal_fields.keys()]
+
+    if missing_fields:
+        print(
+            f"The mandatory field(s): {missing_fields}\n",
+            f"is/are missing in {pov_infile}\n"
+            "No pollen calibration is done until this is fixed!\n"
+            "Pollen are still calculated but this should be fixed "
+            "within a few days.",
+        )
+        sys.exit(1)
+    else:
+        print("All mandatory fields have been read from pov_infile.")
+
+
 def to_grib(inp: str, outp: str, dict_fields: dict, hour_incr: int) -> None:
     """Output fields to a GRIB file.