PROGRAM OPERATIONS AND STANDARDS OBSERVATIONS SPECIFICATION

Transcription

1 PROGRAM OPERATIONS AND STANDARDS OBSERVATIONS SPECIFICATION AMDAR AAA Version 3.0 Software Requirements Specification Author Dean Lockett Program Operations and Standards 23 November 2006 Authorisation Roger Atkinson Supervisor Program Operations & Standards Surface Based Observations Section Distribution( ): STNM, STOS SROO, SRFO, SMMO, SRLR, SRUM STCC, SRDM, SRDS, SRCA File: 30/ Pages

2 Revisions Version Date Author Content Original 28/6/2006 Dean Lockett 1 st Draft /7/2006 Dean Lockett Update for review by AMDAR Panel TC /7/2006 Dean Lockett Update for inclusion of smoothing elements /11/2006 Dean Lockett Update for review by AMDAR Panel TC and format as Bureau Observations Specification Page 2 of 10

3 1. BACKGROUND This document provides a software requirements specification that will be known as AAA Version 3.0. This specification relies on both the ASDAR Specification 1 and the E-AMDAR AAA Version 2.0 Specification 2 (AAA V2) and is defined by providing details of those requirements that constitute additions, deletions or alterations to the preceding specifications. 2. REQUIREMENTS 2.1 AMENDMENTS/ADDITIONS /CORRECTIONS TO E-AMDAR AAA VERSION 2.0 SPECIFICATION The document: Ammendments/Additions/Corrections to Specification , FC Tamis, AirDatec, Revision Status B, 2 April, 2003 should be adopted in whole as requirements to be met within AAA Version REPORTING OF ATMOSPHERIC WATER VAPOUR CONTENT Water vapour content is to be incorporated as an additional observed variable because several airlines are about to commence installation of water vapour sensors. Although only one type of sensor is available at the time this specification was prepared (known as the water vapour sensing system, version 2 or WVSSII), others are under development. Water vapour content will be reported in the downlink message as nnnq. Where nnn is the coded water vapour content encoded as defined below and Q is a quality control parameter. The value of Q will be dependent on the type of sensor employed and the units in which the water vapour content is reported. The software will require a configuration parameter to determine from which sensor the water vapour content should be acquired and, as a consequence, how the water vapour content should be encoded. Water Vapour Sensor Configuration Parameter Downlink Format (nnn) QC Format (Q) None 0 /// / WVSSII 1 Mixing ratio See table 2? 2 Humidity U? 3 Dew point temperature D Table 1 Depending on the water vapour sensor employed, the AAA software will be capable of reporting atmospheric water vapour content for downlink in 3 ways: 1 Software Requirements Specification for the ASDAR Project, Issue 3, Matra Marconi Space UK Limited, October 1994 (reference ). 2 EUMETNET AMDAR AAA AMDAR Software Developments Technical Specification, Version 2, 1 August Page 3 of 10

4 1) Mixing ratio (r): defined to be the ratio of the mass of water vapour content to the mass of dry air of an air sample. The units of r are g/kg. Resolution: 1 x 10-3 g/kg. Range: 0 to 38 g/kg. 2) Relative humidity (RH): defined to be the density of water vapour present in the atmosphere expressed as a percentage of the density of water vapour present when the air sample is saturated (air pressure and temperature held constant). That is: RH = 100 x (density of actual water vapour / density of saturated water vapour) Resolution: 0.1%. Range: 0 to 100% 3) Dew point temperature (DPT): the temperature to which air must be cooled in order for it to become saturated (air pressure held constant. The units of DPT are degrees Celsius ( C). Resolution: 0.1C Range: -100 to 40C Note: In order to obtain the highest quality water vapour content data on the ground, it is always preferable to downlink the water vapour sensor output variable as provided rather than converting to one of the two alternative derived variables, eg. if the sensor provides mixing ratio, then that is what should be reported rather than converting to relative humidity or dew point temperature for reporting. Conversion to an alternative variable can have the effect of reducing both observation resolution and accuracy The WVSSII Sensor Output from the SpectraSensors WVSSII sensor should be extracted according to the manufacturer s specifications with the downlink output expressed as a mixing ratio as defined below. Reporting of Mixing Ratio The mixing ratio derived from the WVSSII sensor will be reported as nnn using the following steps: Step 1: If necessary, convert the mixing ratio to g/kg. e.g. Mixing ratio input = kg/kg = g/kg; Step 2: Round to nearest one thousandth of a g/kg. e.g g/kg rounds to: g/kg [Let this value = MR] Step 3: Multiply by 1000 (express in thousandths of g/kg) [Let this value = MR*] e.g g/kg = 1235 (g/kg)x10 3 ; i.e. MR* = 1235 Step 4: Encode MR* as nnn using the Base 40 compression technique. Calculation of Relative Humidity Although not a component of the down-link AMDAR observation, the relative humidity is to be calculated as a quality control variable for assessing the validity of the WVSSII mixing ratio output. The RH is calculated using the following steps: Page 4 of 10

5 Step 1. Calculate water vapour pressure (e) from equation (a): e = ( PS )( r) /( r ) (a) Step 2. Calculate saturation vapour pressure (e s ) from equation (b): e = 10 s A where: A ( T s ) ( T 35.85) (b) = s Step 3. Calculate RH from equation (c): RH = 100( e es ) (c) Where: P s = static pressure expressed in Pascals T s = static temperature expressed in degrees Kelvin = T sc T sc =static air temperature (SAT) expressed in degrees Celsius Determination of Quality Control Parameter Q and Mixing Ratio Encoding The value of the quality control parameter Q and the encoding of mixing ratio shall be according to the specification in Table 2. WVSS System State Software Logic Q nnn Normal operation Air/Ground = Air 0 Mixing ratio Calculated RH > 100% RH > 100% 1 Mixing ratio Input laser power low Laser < 10% of initial power 2 /// Probe WV temp. input out of range Proprietary Information 3 /// Prove WV pressure input out of range Proprietary Information 4 /// Spectral line shift, missing Proprietary Information 5 /// No laser output Proprietary Information 6 /// Not defined 7 /// Numeric error e.g. divide by zero 8 /// No WVSS installed No WVSS installed / /// Table CHANGES TO MESSAGE DOWNLINK FORMAT TO ACCOMMODATE WATER VAPOUR CONTENT To include water vapour content within the downlink message it will be necessary to define a modified AMDAR format, which will be labelled with AMDAR3 within section 1 of the AMDAR message block. The water vapour content is to be incorporated as an additional element within each observation. In the terms used within AAA V2, the water vapour content will always be provided as type absolute and will be 4 characters in length (nnnq). Page 5 of 10

6 Table 3 provides the description of the water vapour element within the observation in a similar format to that provided within section of AAA V2. Description Type Absolute Range Delta Allowed Range First record characters Original Elements AAA V2 AAA V2 AAA V Water Vapour (mixing ratio) 8 absolute 0 to thousandths of g/kg. Water Vapour (humidity) 8 absolute 0 to 1000 tenths of % Water Vapour (dew point) 8 absolute -100 to +40 tenths of C Table 3 N/A N/A N/A 4 4 Total Subsequent record characters The addition of the water vapour element increases the length of the first observation in each message block to 27 characters and the length of subsequent ( relative ) observations to 22 characters. This means that a message block will now contain 4 lines, each containing 2 observations (total of 8 observations which includes a first absolute observation followed by 7 relative observations): Section Description Characters 1 Header 14 2 Line 1: Observations (CRLF) = 51 2 Line 2: Observations (CRLF) = 46 2 Line 3: Observations (CRLF) = 46 2 Line 4: Observations (CRLF) = 46 Total 203 Table 4 An AMDAR3 message block will report 8 observations rather than the 9 observations reported within the AMDAR2 message block. 2.4 QUALITY CONTROL, SMOOTHING AND PROCESSING OF DATA ELEMENTS Range Checks It is assumed that a range check is applied to all elements according to the allowable ranges defined in AAAV2. In the case that a particular parameter has the arithmetic mean smoothing function applied, the range check should be applied to each data sample at the highest available sampling frequency (S Hz). Page 6 of 10

7 2.4.2 Temperature Quality Control Function It is assumed that the quality control check for temperature as specified in section of the ASDAR specification is applied. In the case that the arithmetic mean smoothing function is applied to temperature, this QC function should be applied to each data sample at the highest available sampling frequency Modification and Addition to Smoothing Function Application The smoothing function as applied within the AAA V2 specification will be implemented as an optional smoothing function. An additional smoothing function as specified below will also be implemented as a 2 nd option. A 3 rd option will be available for no smoothing to be applied. When a smoothing function is applied it must be applied to all reported meteorological variables as set out in table 5. Smoothing functions will be parameterised, with both the application of the smoothing function and the time constant T (for both ascent or descent, T p and cruise, T c ) made uplink controllable Arithmetic Mean Smoothing Function The arithmetic mean smoothing function will initially be applied as the default smoothing option. Once the smoothing function option is altered (e.g. by uplink command) the new setting will remain in place until manually altered. The arithmetic mean smoothing function is defined below: For an element at observation time t and with time constant T (seconds) and sampling rate S Hz (T will always be S): The value of the element at Y t can be calculated after T/2 seconds. The potential number of valid samples available will be S*T + 1 = n #. The sample set from which the smoothed value is calculated will include all valid samples in the timeframe t T/2 to t + T/2 and consists of y 1,y 2,.,y n (n n # ). Therefore the smoothed data value at time t will be: Y = 1 / n t n i= 1 Yi The value Y t is valid and reported only if n/n # 0.5 (i.e. at least 50% of expected samples). T should be Selection of Instantaneous Values When an element of an observation is not smoothed, an instantaneous value should be obtained that is as close to the observation time as possible and within ±T i seconds. If a sample is not available within the allowable time frame, i.e. t T i to t + T i, then the element should be reported as missing. T i will be an uplink-controllable parameter with default initial setting of Data Processing Table 5 shows the processing requirements for each element within the AMDAR observation. Page 7 of 10

8 Element Smoothing Activation Default Default Time Constant for Profile Observations: T p Default Time Constant for Cruise Observations: T c Instantaneous Time Constant: T i Latitude N/A N/A N/A 1 Longitude N/A N/A N/A 1 Pressure altitude Activate Temperature Activate Wind Direction Activate Wind Speed Activate DEVG Activate Water vapour (MR) Water vapour (DP) Water vapour (RH) Notes: Activate Activate Activate Table 5 N/A (not applicable) indicates these elements should not be smoothed (i.e. instantaneous values only should be reported). T p and T c will be constants across all elements other than DEVG and only DEVG will have separate uplink controllability. For DEVG, T p and T c will always be set the same. T i will be constant across all elements. Deactivation of smoothing will be applied for all elements, i.e. smoothing is either activated for all elements (other than latitude and longitude) or deactivated for all elements. 2.5 CHANGES TO UPLINK FORMAT FOR ADDITIONAL CONFIGURATION COMMANDS The following additional permanent uplink commands will be required to facilitate the optional smoothing functionality requested: Command Description Default Set smoothing function Configures the smoothing algorithm to be used. Options are: 1) Arithmetic mean; 2) ASDAR; Arithmetic Mean. Page 8 of 10

9 Set smoothing time constants Set instantaneous time constant 3) Deactivated. Allows adjustment of the profile and cruise time constants used by the smoothing functions. Allows adjustment of the instantaneous time constant (see section 2.4.5) Table 6 Page 9 of 10 See Table 5. See Table 5. The command functionality and mnemonic should adhere as closely as possible to that adopted within AAA V CHANGES TO DATA OPTIMISATION FUNCTIONS Geographical Data Control Boxes Increase to 10 boxes Airport Specific Reporting Increase to 50 airports. 2.7 CHANGES TO AIRCRAFT STATUS REPORT FORMAT Changes to the aircraft status report format have been highlighted in red. The AMDARSTATUS3 tag identifies the status report as formatted according to AAAV3 specification. QU QUKAXBA }.QXSXMXS } Header locally generated DFD } FI BA2576/AN G-DOCB } DT QXS MXP D77A } - AMDARSTATUS3 IA I A AS A Int A1 /Int A2 RS R Int R D Int D1 / Int D2 T1T L1 T2T L2 N SInt s SPInt TP SCInt TC SDInt TD IInt I BB N Lat Y1 /Long X1 Lat Y2 /Long X2 S B } BB N Lat Y1 /Long X1 Lat Y2 /Long X2 S B } Information for active (of possible 10) boxes } provided. BB N Lat Y1 /Long X1 Lat Y2 /Long X2 S B } Positions of active (of possible 50) AA N Lat N /Long N /S A AA N Lat N /Long N /S A } airports listed, AA N Lat N /Long N /S A AA N Lat N /Long N /S A } 2 on each line The Bold and / characters in the example are fixed group identifiers. Parameter I A I A S A Description AMDAR Identifier (Max 8 characters) Ascent phase reporting status: R = Reporting active

10 D = Disabled Int A1 Observing Interval during ascent phase A1, in hpa Int A2 Observing Interval during ascent phase A2, in hpa S R Level flight phase reporting status: R = Reporting active D = Disabled Int R Observing interval during level flight in seconds S D Descent phase reporting status: R = Reporting active D = Disabled Int D1 Observing Interval during ascent phase D1, in hpa Int D2 Observing Interval during ascent phase D2, in hpa T L1 Trigger level 1 setting in hpa T L2 Trigger level 2 setting in hpa N The number of observations made during intervals A1 and A2 Int s Smoothing method in operation: 0 = none 1 = ASDAR 2 = arithmetic mean Int TP Profile time constant for smoothing Int TC Cruise time constant for smoothing Int TD Time constant for DEVG Int I Instantaneous time constant B N Geographical box number (1 to 10) Lat Y1 Latitude value Y1 applied to box B N in degrees & minutes (ie = S) Long X1 Longitude value X1 applied to box B N Lat Y2 Latitude value Y2 applied to box B N Long X2 Longitude value X2 applied to box B N S B Status of box B n (R = Reporting active, D= Reporting disabled) A N Airport number (1-20) Lat N Latitude of airport number A n Long N Longitude setting for airport number A N Status of airport (R = Reporting active, D = Reporting disabled) S A Notes: The status report only outputs those airports and geographic boxes that are activated. Page 10 of 10