This note synthesises the empirical comparison between IRI-2020 model predictions and GNSS Radio Occultation observations over the Indonesian region. It is a comparison note, not a standalone authority on either the model or the technique.
Boundary:
It does not restate the full IRI model specification.
It does not claim that the sampled days represent all Indonesian conditions.
It links empirical findings to SBAS integrity implications in the vault.
Comparison dimensions
Overall error summary (initial 5-day study)
Metric
Value
Interpretation
Bias
66.72 TECU
IRI underestimates TEC by 66.72 TECU on average
RMSE
94.34 TECU
Total error magnitude
MAE
67.01 TECU
Average absolute error
MAPE
87.6%
Mean percentage error
Correlation (r)
0.4146
Weak positive correlation
R²
−0.7309
Model performs worse than predicting the mean
Monthly variation
Month
Bias (TECU)
RMSE (TECU)
January
83.7
108.7
February
70.2
91.9
March
72.5
113.2
April
75.8
102.3
May
48.0
69.4
Altitude dependence
Errors are largest at lower occultation heights (near the F2 layer peak):
Altitude (km)
Bias (TECU)
350–400
126.0
400–450
77.9
500–550
47.9
550–600
33.8
Spatial variation
Region
Bias (TECU)
RMSE (TECU)
Western (Sumatra/Java)
98.0
122.7
Central (Kalimantan)
114.8
148.2
Eastern (Sulawesi/Papua)
106.6
145.3
What this comparison implies
Systematic underestimate, not random scatter — IRI-2020 consistently underpredicts TEC in the Indonesian equatorial region.
Altitude sensitivity — The largest errors occur near the F2 peak height, suggesting the model’s vertical profile parameterization is misaligned with actual equatorial conditions.
Spatial heterogeneity matters — Central Indonesia (Kalimantan) shows the largest errors, likely due to EIA crest proximity.
Temporal gaps are integrity-relevant — No post-sunset (18–21 LT) profiles means the most challenging equatorial conditions are unobserved in this dataset.