FAQs about the Service¶
How soon after observation is data available with the Near-Real-Time service?¶
As soon as the satellite data has been transferred from the satellite to the ground segments, VanderSat needs about an hour before this data is transformed into soil moisture data. Generally this is within 6 hours after the satellite has observed an area, given that the satellite system is fully operational.
When is my data available after the start of the contract?¶
Generally, this depends on whether this region has been processed before or not. Processing a region requires a great deal of processing, which means that only those parts of the world are updated where clients have requested data. If a new area needs to be processed, especially when the full archive is requested, the data needs to be checked for error sources. After this, an account is created and set up for use. At the moment, we strive to deliver an archive within two weeks. If one only needs a Near-Real-Time service, the required time can be reduced significantly.
Do you need in-situ data in order to start processing a region anywhere in the world?¶
No. The Land Parameter Retrieval Model (Where can I find how your soil moisture retrieval works?) relies on physical quantities that can be directly inferred from satellite measurements.
What is the coverage of the data in terms of observations?¶
Each satellite observes the globe each day, as their orbit is synchronized with the sun moving from east to west as it orbits from pole to pole in about 90 minutes (sun-synchronous orbit). Nevertheless, not every single area is observed daily since the satellite’s field of view is not wide enough. This results in less frequent measurements around the equator, where the Earth is ‘widest’ around its longitude belt, and more frequent measurements at high latitudes (in absolute values), where the longitude belts are less wide. One can expect between 200 and 330 measurements per satellite, per year, depending on geographical location.
Are there any weather conditions for which no valid measurements can be derived?¶
Most conditions are suitable for deriving a measurement, especially cloudy conditions are generally not a problem. There are however exceptions related to frozen conditions. When the soil is frozen, the signal that the satellite observes is completely different from unfrozen soil and cannot be transformed into soil moisture. This also applies for heavy thunderstorms when the top of the clouds are frozen. More information can be found in the documentation describing our data flags (How to retrieve the data flags?).
Are there any other conditions for which no valid measurements can be derived?¶
This can happen when there are radio sources transmitting on the same frequency as the satellite is measuring. As a result, the measurement can be disturbed, causing the soil to look drier than it actually is. This disturbance is called Radio Frequency Interference (RFI). We have a filter in place that checks for these disturbances to filter them out in an early stage of the processing chain. However, when areas become too obscured by RFI, the soil moisture retrieval will eventually fail. More information can be found in the documentation describing our data flags (How to retrieve the data flags?).