Since we estimate the glacier velocity using offset tracking method for a dual pol SAR (S1A GRD) datasets. How can i estimate the resultant velocity to yearly basis? also how can i verify it?
Roma Mevadawala
Understand Your Velocity Data Units: Offset tracking typically provides velocity in meters per time interval, depending on the temporal separation between the two images used (e.g., 6 or 12 days, depending on the Sentinel-1 revisit time). The result is usually in meters per day (m/day). Determine the Time Interval (Δt): Calculate the time interval between the acquisition dates of the image pair used in the offset tracking. This is typically the temporal baseline of the interferometric pair. For Sentinel-1, common intervals are:6 days for standard ascending or descending pairs. 12 days if you’re combining ascending and descending passes or certain revisit pairs. Vdaily=DisplacementΔtV_{\text{daily}} = \frac{\text{Displacement}}{\Delta t}Vdaily=ΔtDisplacementCalculate the Average Daily Velocity: Offset tracking directly provides glacier displacement between two time points, typically in meters. Divide this displacement by the number of days between the images to get the daily velocity: Convert to Yearly Velocity: Multiply the daily velocity by 365.25 (considering leap years):Vyearly=Vdaily×365.25V_{\text{yearly}} = V_{\text{daily}} \times 365.25Vyearly=Vdaily×365.25This gives you the yearly glacier velocity in meters per year (m/year). Calculate the daily velocity: Vdaily=186=3 m/dayV_{\text{daily}} = \frac{18}{6} = 3 \, \text{m/day}Vdaily=618=3m/day Convert to yearly velocity: Vyearly=3×365.25=1095.75 m/yearV_{\text{yearly}} = 3 \times 365.25 = 1095.75 \, \text{m/year}Vyearly=3×365.25=1095.75m/year
To convert offset tracking-based glacier velocity from Sentinel-1A GRD data to a yearly velocity, follow these steps:
Example Calculation
Assume:
- Displacement from offset tracking = 18 meters over a 6-day interval.
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