BALTRAD

1. Algorithm name

Quality-based Echo Top (ETOP) product generation – Product2D: ETOP

2. Basic description

a) Physical basis of the algorithm

The algorithm generates Echo Top (ETOP) 2-D product from radar reflectivity volume with quality information using product2D_PPI algorithm.

b) Amount of validation performed so far

Not performed yet.

c) References (names and contact information of all developers during the evolutionary history, scientific papers)

IMGW, Department of Ground Based Remote Sensing.

3. ODIM metadata requirements for I/O

Input data: VOL

• General “what”: source(NOD).
• For particular SCANs:
  • Dataset-specific “where” for data and QI: nbins, nrays.
  • Data-specific “what” for data: gain, offset, nodata, undetect.
  • Data-specific “what” for QI: gain, offset, nodata, undetect.

Output data: Cartesian data

• Top-level “where”: lon, lat, xsize, ysize, xscale, yscale.
• Dataset-specific “what”: product.
• Data-specific “what” for data: gain, offset, nodata, undetect.
• Data-specific “what” for QI: gain, offset, nodata, undetect.

4. Input data

a) What kind of radar data (including the list of previous algorithms and quality flags applied)

object=PVOL:

• quantity=DBZH, otherwise TH,
• quantity=QIND (generated e.g. by QI_TOTAL algorithm).

b) Other data (optional and mandatory, applying “universally” agreed formats, geometry)

Defined projection and domain of Cartesian output.

5. Logical steps, using any of: text, flow charts, graphics, equations (or references to equations), conditional branches in “all possible cases”.

The algorithm generates Echo Top (ETOP) 2-D products in Cartesian coordinates from radar reflectivity volume and based on the data quality information.

Algorithm parameters

Set of the algorithm parameters:

Description	Denotation	Unit	Default value
Lower height limit for ETOP product generation	ETOP_hMin	km	1
Upper height limit for ETOP product generation	ETOP_hMax	km	20
Minimum cloud reflectivity	ETOP_ZMin	dBZ	4

Algorithm description

Echo Top (ETOP) product represents Cartesian image of height of echo (cloud) tops defining cloud boundary with proper level of radar reflectivity Z₀ (in dBZ) (Fig. 1). The ETOP (in km) is detected in a preset range of height (between h_min and h_max) and generally is calculated by interpolation of reflectivity Z between two highest gates for which the reflectivity passes Z,,0,, value. If searched height of Z₀ value is between two measurements Z’ and Z” detected at heights h’ and h” respectively, then in order to find the height h_int at which echo top occurs (Z = Z₀) the linear interpolation is applied:

In case when both considered measurements are with echo (Z ≥ Z₀) then _h_{int_ = min (hmax, max (h’, h”)).}

Fig. 1. Scheme of generation of radar Echo Top product (ETOP).

There are considered only measurements (Cartesian pixels on PPIs) between h,,min,, and h,,max,,, and two closest ones (below h_min and above h_max). At first, height h of the highest measurement with echo (Z ≥ Z₀) is found.

The following cases may occur:

• h > h_max and lower measurement exists, then echo top h_int is interpolated from the two measurements, and:
  • if h_int > h_max then ETOP = “undetect” and lower echo (Z ≥ Z₀) is analyzed if exists,
  • if h_int <h_max.

• h > h_max and lower measurement does not exist, then ETOP = “nodata”.

• h <= h_max and higher measurement exists, then echo top h_int is interpolated from the two measurements, and:
  • if h_int ≥ h_min then ETOP = min (h_int, h_max),
  • if h_int < h_min then ETOP = “undetect”.
• h <= h_max and higher measurement does not exist, then:
  • if h ≥ h_min then ETOP = h,
  • if h < h_min then ETOP = “nodata”.

Otherwise, i.e. echo (Z ≥ Z₀) is not found, then:

• if there so no measurement between h_min and h_max then ETOP = “nodata”,
• else ETOP = “undetect”.

Data quality characterization

Quality of the ETOP depends on the two factors:

• quality of reflectivity data from which ETOP was determined, QI_source,
• how large fraction of investigated heights (between h_min and h_max) was scanned, QI_scope,

and the final quality index QI is taken as a product of the both factors:

The value of the first component QI_source is taken as the quality of the measurement defining echo top, and in case of interpolation from two measurements the minimum quality is chosen. If ETOP “nodata”, and if ETOP 1.

Fig. 2. Quality characterization for Echo Top product in terms of availability.

The second component QI_scope is determined based on heights of the highest and lowest scans for considered Cartesian pixel (h_highest and h_lowest respectively) in relation to h_min and h_max (Fig. 2):

• if h_highest < h_min then

  _ QI _scope _ “nodata”.

• if h_highest ≥ h_min and h_lowest <= h_max then QI_scope depends on what part of height range between h_min and h_max was scanned:

but if (_ h_highest_ > h_max ) and (ETOP <> “undetect”) then QI_scope = 1.

• if h_lowest > h_max then

  QI_scope “nodata”.

6. Output

a) Data type using ODIM notation where possible, e.g. DBZH

Input quantity as IMAGE object (in Cartesian coordinates) with:

• “how”: task - “pl.imgw.product2d.etop”,
• “how”: task_args
  • parameters inherited from PPI algorithm (interpolation method and selected quality field name),
  • parameters of ETOP algorithm,

b) Quality index (QI) field

Quality index field QIND as IMAGE object with:

• “how”: task - “pl.imgw.product2d.etop”,
• “how”: task_args - parameters inherited from PPI algorithm (interpolation method and selected quality field name).

7. Outline of a test concept exemplifying the algorithm, as a suggestion for checking that an implementation has been successful.

TBD