HDF5 File Structure

Sensor raw data are stored in HDF5 files.

Directory Structure

Sensors are grouped according to their sensor name. Integrations are stored as datasets in a subgroup called Rawdata. The name of a dataset is a combination of its timestamp and integration counter.

HDF5 directory structure.

Each dataset (integration) is a 6 x 256 array. Each dataset contains six 256-channel spectra for cal_HH, cal_VV, data_HH, data_VV, data_U, and data_V:

• cal_HH, cal_VV: auto-correlation products of the calibration load

• data_HH, data_VV: auto-correlations products of the soil signal

• data_U, data_V: cross-correlations products of the soil signal

Data array.

Datasets

Each integration is stored with a set of metadata. Most of the metadata fields are self-explanatory, except for the following ones:

• accelerometer: A 3-element array containing the output of the accelerometer for the x, y, and z-axis. The look angle of the sensor is $\tan\alpha = \dfrac{a[2]}{a[1]}$.

• bw_mhz: Sensor bandwidth in MHz.

• course_deg: GPS course (azimuth) in degrees.

• flight_counter: A counter that increases when the drone returns to its "home" position. This can be used to identify battery swaps.

• freq_mhz: Sensor centre frequency in MHz.

• gyro: A 3-element array containing the gyroscope output for the x, y, and z-axis.

• integration: Counter increases for each new integration containing cal-load and soil signal.

• lna_temperature_degC: The physical temperature of the calibration load in degrees Celsius.

• runtime: Sensor runtime since powerup in milliseconds.

• sats: 2-element array containing the number of GPS satellites used and visible.

• sf_mhz: Sampling frequency in MHz. The frequency of each channel is: $f(\mathrm{MHz}) = \mathrm{freq\_mhz} - \mathrm{sf\_mhz}/4 + \mathrm{channel} \cdot (\mathrm{sf\_mhz}/2)/256$

• speed_kmh: GPS speed in km/h.

Metadata for each integration.