SoilMoisture.md

Soil Moisture

A collection of soil moisture specific quality check routines.

Index

• sm_flagSpikes
• sm_flagBreaks
• sm_flagConstants
• sm_flagFrost
• sm_flagPrecipitation
• sm_flagRandomForest

sm_flagSpikes

sm_flagSpikes(raise_factor=0.15, deriv_factor=0.2,
              noise_func="CoVar", noise_window="12h", noise_thresh=1,
              smooth_window="3h", smooth_poly_deg=2)

parameter	data type	default value
raise_factor	float	0.15
deriv_factor	float	0.2
noise_func	string	"CoVar"
noise_window	offset string	"12h"
noise_thresh	float	1
smooth_window	offset string	"3h"
smooth_poly_deg	integer	2

The function is a wrapper around spikes_flagSpektrumBased with a set of default parameters referring to [1]. For a complete description of the algorithm and the available parameters please refer to the documentation of flagSpikes_spektrumBased

[1] Dorigo, W. et al: Global Automated Quality Control of In Situ Soil Moisture Data from the international Soil Moisture Network. 2013. Vadoze Zone J. doi:10.2136/vzj2012.0097.

sm_flagBreaks

sm_flagBreaks(thresh_rel=0.1, thresh_abs=0.01,
              first_der_factor=10, first_der_window="12h",
              scnd_der_ratio_range=0.05, scnd_der_ratio_thresh=10,
              smooth=False, smooth_window="3h", smooth_poly_deg=2)

parameter	data type	default value
thresh_rel	float	0.1
thresh_abs	float	0.01
first_der_factor	float	10
first_der_window	offset string	"12h"
scnd_der_ratio_range	float	0.05
scnd_der_ratio_thresh	float	10.0
smooth	bool	False
smooth_window	offset string	"3h"
smooth_poly_deg	integer	2

The function is a wrapper around breaks_flagSpektrumBased with a set of default parameters referring to [1]. For a complete description of the algorithm and the available parameters please refer to the documentation of breaks_spektrumBased.

[1] Dorigo, W. et al: Global Automated Quality Control of In Situ Soil Moisture Data from the international Soil Moisture Network. 2013. Vadoze Zone J. doi:10.2136/vzj2012.0097.

sm_flagConstants

sm_flagConstants(window="12h", thresh=0.0005,
                 precipitation_window="12h",
                 tolerance=0.95,
                 deriv_max=0.0025, deriv_min=0,
                 max_missing=None, max_consec_missing=None,
                 smooth_window=None, smooth_poly_deg=2)

parameter	data type	default value	description
window	offset string	"12h"	Minimum duration during which values need to identical to become plateau candidates. See condition (1)
thresh	float	0.0005	Maximum variance of a group of values to still consider them constant. See condition (2)
precipitation_window	offset string	"12h"	See condition (3) and (4)
tolerance	float	0.95	Tolerance factor, see condition (5)
deriv_max	float	0	See condition (4)
deriv_min	float	0.0025	See condition (3)
max_missing	integer	None	Maximum number of missing values allowed in window, by default this condition is ignored
max_consec_missing	integer	None	Maximum number of consecutive missing values allowed in window, by default this condition is ignored
smooth_window	offset string	None	Size of the smoothing window of the Savitsky-Golay filter. The default value None results in a window of two times the sampling rate (i.e. three values)
smooth_poly_deg	integer	2	Degree of the polynomial used for smoothing with the Savitsky-Golay filter

This function flags plateaus/series of constant values in soil moisture data.

The function represents a stricter version of constants_flagVarianceBased. The additional constraints (3)-(5), are designed to match the special cases of constant values in soil moisture measurements and basically for preceding precipitation events (conditions (3) and (4)) and certain plateau level (condition (5)).

Any set of consecutive values

$x_k,..., x_{k+n}$

, of a time series

x

is flagged, if:

1. n >
   window
2. \sigma(x_k, x_{k+1},..., x_{k+n}) <
   thresh
3. \max(x'_{k-n-s}, x'_{k-n-s+1},..., x'_{k-n+s}) \geq
   deriv_min, with
   s
   denoting periods per precipitation_window
4. \min(x'_{k-n-s}, x'_{k-n-s+1},..., x'_{k-n+s}) \leq
   deriv_max, with
   s
   denoting periods per precipitation_window
5. \mu(x_k, x_{k+1},..., x_{k+n}) \le \max(x) \cdot
   tolerance

NOTE:

• The time series is expected to be harmonized to an equidistant frequency grid

This function is based on [1] and all default parameter values are taken from this publication.

[1] Dorigo, W. et al: Global Automated Quality Control of In Situ Soil Moisture Data from the international Soil Moisture Network. 2013. Vadoze Zone J. doi:10.2136/vzj2012.0097.

sm_flagFrost

sm_flagFrost(soil_temp_variable, window="1h", frost_thresh=0)

parameter	data type	default value	description
soil_temp_variable	string		Name of the soil temperature variable in the dataset
window	offset string	"1h"	Window around a value checked for frost events
frost_thresh	float	0	Soil temperature below frost_thresh are considered as frost

This function flags soil moisture values if the soil temperature (given in soil_temp_variable) drops below frost_thresh within a period of +/- window.

This function is an implementation of the soil temperature based flagging presented in [1] and all default parameter values are taken from this publication.

[1] Dorigo, W. et al: Global Automated Quality Control of In Situ Soil Moisture Data from the international Soil Moisture Network. 2013. Vadoze Zone J. doi:10.2136/vzj2012.0097.

sm_flagPrecipitation

sn_flagPrecipitation(prec_variable, 
                     raise_window=None,
                     sensor_depth=0, sensor_accuracy=0, 
                     soil_porosity=0,
                     std_factor=2, std_window="24h"
                     ignore_missing=False)

parameter	data type	default value	description
prec_variable	string		Name of the precipitation variable in the dataset
raise_window	offset string	None	Duration during which a rise has to occur
sensor_depth	float	0	Depth of the soil moisture sensor in meter
sensor_accuracy	float	0	Soil moisture sensor accuracy in \frac{m^3}{m^{-3}}
soil_porosity	float	0	Porosity of the soil surrounding the soil moisture sensor
std_factor	integer	2	See condition (2)
std_window	offset string	"24h"	See condition (2)
ignore_missing	bool	False	Whether to check values even if there is invalid data within std_window

This function flags rises in soil moisture data if there are no sufficiently large precipitation events in the preceding 24 hours.

A data point

x_k

of a time series

x

with sampling rate

f

is flagged, if:

1. x_k
   represents a rise in soil moisture, i.e. for
   s =
   (raise_window /
   f
   ):
   x_k > x_{k-s}

2. The rise is sufficiently large and exceeds a threshold based on the standard deviation

   \sigma
   of the values in the preceding std_window, i.e. the following condition is fulfilled for
   h =
   std_window /
   f
   :
   x_k - x_{k-s} >
   std_factor
   \cdot \sigma(x_{t-h},...,x_{k})

3. The total amount of precipitation within the last 24 hours does not exceed a certain threshold, i.e. with

   j =
   "24h" /
   f
   the following condition is fulfilled:
   y_{k-j} + y_{k-j+1} + ... + y_{k} \le
   sensor_depth
   \cdot
   sensor_accuracy
   \cdot
   soil_porosity

This function is an implementation of the precipitation based flagging presented in [1] and all default parameter values are taken from this publication.

[1] Dorigo, W. et al: Global Automated Quality Control of In Situ Soil Moisture Data from the international Soil Moisture Network. 2013. Vadoze Zone J. doi:10.2136/vzj2012.0097.

sm_flagRandomForest

sm_flagRandomForest(references, window_values, window_flags, path)

parameter	data type	default value	description
references	string or list of strings		the field names of the data series that should be used as reference variables
window_values	integer		Window size that is used to derive the gradients of both the field- and reference-series inside the moving window
window_flags	integer		Window size that is used to count the surrounding automatic flags that have been set before
path	string		Path to the respective model object, i.e. its name and the respective value of the grouping variable. e.g. "models/model_0.2.pkl"

This function uses pre-trained machine-learning model objects for flagging. This requires training a model by use of the training script provided. For flagging, inputs to the model are the data of the variable of interest, data of reference variables and the automatic flags that were assigned by other tests inside SaQC. Therefore, this function should be executed after all other tests. Internally, context information for each point is gathered in form of moving windows. The size of the moving windows for counting of the surrounding automatic flags and for calculation of gradients in the data is specified by the user during model training. For the model to work, the parameters 'references', 'window_values' and 'window_flags' have to be set to the same values as during training. For a more detailed description of the modeling approach see the training script.