Predicting Visibility from Kd490 (Water Turbidity Index): Satellite Data Power
2026-03-16
Kd490 (diffuse attenuation coefficient at 490nm) measures how quickly light diminishes in seawater. Measured by NOAA satellites from space, higher values indicate more turbid water. In our AI visibility prediction model, Kd490 ranks as the #3 most important feature, demonstrating that satellite data can meaningfully contribute to practical visibility forecasting.
20.9m
Kd490 < 0.05
14.2m
Kd490 0.05–0.1
8.9m
Kd490 > 0.2
#3
AI importance rank
Average Visibility by Kd490 Range
| Kd490 Range | Avg Vis (m) | Difference |
|---|---|---|
| < 0.05 (very clear) | 20.9m | baseline |
| 0.05–0.1 (clear) | 14.2m | −6.7m |
| 0.1–0.2 (moderate) | 11.3m | −9.6m |
| > 0.2 (turbid) | 8.9m | −12.0m |
Waters with Kd490 below 0.05 average 20.9m visibility, while those above 0.2 average just 8.9m — a 12m difference. This predictive power from a single satellite metric is remarkable.
What Is Kd490: A Diver's Explanation
Physical meaning
Kd490 measures how quickly 490nm (blue) light attenuates with depth. Units are 1/m (per meter). Lower values mean light penetrates deeper — i.e., clearer water.
How it's measured
NOAA satellites (VIIRS/SNPP etc.) observe ocean color from space and calculate Kd490 using ocean color algorithms. Updated daily on cloud-free days and freely available. Our project fetches data from NOAA ERDDAP.
Relation to diving
Since Kd490 reflects suspended particles and plankton in the water, it correlates strongly with the 'visibility' divers experience. Checking NOAA satellite imagery before a dive can give you a rough preview of conditions.
Kd490 Importance in the AI Model
In our LightGBM model (R²=0.824), Kd490 ranks #3 among 45 features. The top two are temporal features (month, day of year), but among environmental data, Kd490 has the strongest predictive power.
Why Kd490 Works Well
- Physically linked to visibility (light attenuation)
- Integrates effects of weather, rainfall, and plankton
- Captures localized coastal changes
- Log-transformed (kd490_log) for near-normal distribution
Practical Guide: Check Kd490 Before Your Dive
Step 1: Access NOAA CoastWatch
Through NOAA CoastWatch (coastwatch.pfeg.noaa.gov) ERDDAP, you can freely view Kd490 satellite imagery for waters around Japan.
Step 2: Check your destination's value
Kd490 below 0.05 suggests 20m-class visibility. Above 0.1, expect around 10m. Above 0.2 indicates quite turbid conditions.
Step 3: Caveats
Satellite data is unavailable under cloud cover. Also, very shallow coastal areas may have reduced accuracy due to seafloor reflections. Looking at multi-day averages provides more reliable assessments.
Limitations of Kd490
Kd490 is a powerful indicator but not perfect. Sand stirred up near the seafloor and localized tidal current effects are invisible to satellites. Additionally, the visibility divers experience varies with depth and light angle. Use Kd490 as a guide and combine it with local dive shop reports for the best assessment.
About the Data
Kd490 data sourced from NOAA ERDDAP (VIIRS/SNPP satellite). Visibility data uses 46,000+ real dive log observations nationwide. Range-based averages calculated by matching satellite data with same-day visibility observations.
References: NASA Ocean Color (https://oceancolor.gsfc.nasa.gov/), NOAA CoastWatch ERDDAP
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