Photosynthetic photon flux density at 47 m
Half-hourly incoming photosynthetic photon flux density at 47 m on the CH-LAE tower, 2004-2025, gap-filled to completeness. The file is 03_METEO_PPFD_IN_GAPFILLED_2004-2025 (parquet and CSV): 385,728 records on a continuous 30-minute middle-timestamp index (named TIMESTAMP_MIDDLE in the file) in local time (UTC+1, no daylight saving), from 2004-01-01 00:15 to 2025-12-31 23:45.
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Method, evidence and checks:
03_METEO_PPFD_IN— builds the product: the merge of the two screenings, the 2012 corrections, the nighttime offset, the gap-filling, and the section identifying the sensor and testing it at both hardware changes.RADIATION_SENSOR_CONTINUITY— compares four radiation sensors and attributes every level change in the record to a particular instrument. It is what places the decline described below on this sensor rather than on either reference.Meteo_Product_Chain— where this product sits in the chain. It depends onSW_IN, which has to be built first.
The 47 m quantum sensor reads progressively lower against both of its independent references from 2022 onwards: about 3 to 4 % lower over 2021-2025, and 6 to 7 % below its 2006-2010 level by the end of the record, which arrives before the decline has levelled off.
It is not corrected, for the reasons under Known limitations. A trend or a period comparison spanning the last years of this record therefore contains the sensor’s own decline as well as any change in the light. Comparisons within a year are unaffected, as is any use of a single half-hour.
One instrument over the whole record, read through the same conversion by two acquisition systems, with no step at either hardware boundary. There is a single value column and no _HOMOGENIZED counterpart. The gradual decline above is not something a boundary correction could address.
Columns
Every one of the 385,728 records carries a value, and the flag is defined everywhere.
03_METEO_PPFD_IN_GAPFILLED_2004-2025.
| column | unit | description |
|---|---|---|
PPFD_IN_T1_47_1_gfXG |
µmol m-2 s-1 | Incoming photosynthetic photon flux density, gaps filled. Complete, non-negative, exactly zero at night. |
FLAG_PPFD_IN_T1_47_1_ISFILLED |
- | Whether the value was measured, and if not, which method produced it. |
FLAG_PPFD_IN_T1_47_1_ISFILLED
Filter on == 0 for measured records. The series is complete, so every other code marks a modelled value.
| code | meaning | records | share |
|---|---|---|---|
| 0 | observed | 369,124 | 95.7 % |
| 1 | daytime gap, filled by the XGBoost model | 8,374 | 2.2 % |
| 2 | daytime gap, filled by the timestamp-only fallback model | 600 | 0.2 % |
| 3 | nighttime gap, set to zero by physics | 7,543 | 2.0 % |
| 4 | short daytime gap, filled by linear interpolation | 87 | 0.02 % |
Code 3 is not an estimate: the sun is below the horizon and the value is zero by physics. Counting codes 0 and 3 together as not modelled raises the non-modelled share to 97.7 %.
The filled records are not spread thinly through the series. They fall in about 160 runs, dominated by the period before the measurement begins and by a small number of outages, so filtering on the flag removes whole periods rather than a sprinkling of half-hours. Sixteen of the twenty-two years carry fewer than a hundred filled records each.
Coverage
The tower measurement begins on 2004-09-20 10:45. Everything before that is modelled.
| year | measured | why |
|---|---|---|
| 2004 | 28 % | the record begins on 20 September |
| 2012 | 93 % | logger clock error, power-supply failure and storm damage |
| 2016 | 94 % | the January outage during which the logger was replaced |
The 2012 faults are the largest interruption inside the measured period. A logger clock error shifted one block of August 2012 by 15.5 hours; a tower power-supply failure in late July and August, and storm damage in late October and November, left records that could not be repaired. The clock error was corrected, the other two periods were removed, and all of it was gap-filled. The three windows are the same ones notebooks 01 and 02 remove, because the fault is in the logger and the power supply and therefore affects every variable on that system.
The January 2016 outage runs from 1 January to 21 January 14:15, when the replacement logger came online.
How the gaps were filled
Daytime gaps are filled by an XGBoost model over the whole record. There is no period split, unlike SW_IN and TA: all three drivers span the full record, so no model is ever asked to predict a period whose drivers it did not see.
The drivers are the gap-filled SW_IN from notebook 01, potential radiation computed from the site coordinates, and MeteoSwiss Lägern global radiation. The tower pyranometer is by far the strongest (same height, same mast, r2 0.99) but it is itself gap-filled, and PPFD_IN gaps tend to coincide with SW_IN gaps because both sensors sit on the same logger. MeteoSwiss Lägern covers that case: an independent measurement of the sky 2.5 km away, at the cost of considerably more scatter. Code 2 marks the few half-hours where neither radiation driver was available.
Nighttime gaps are set to zero rather than modelled. The exported series is always the tower sensor; a reference is a driver and never overwrites a measured value.
Known limitations
The sensor has been losing response since 2022, and it had not levelled off by the end of the record. It falls against the co-located tower pyranometer and against MeteoSwiss Lägern together, by 3.3 % and 3.7 % respectively between 2021 and 2025, reaching 6.1 and 7.4 % below its 2006-2010 level in the last year of the record. Both references moving together is what places the change on this instrument;
RADIATION_SENSOR_CONTINUITYreaches the same conclusion from four sensors at once. It is not corrected, because it develops over years rather than stepping at a date, so there is no boundary at which a correction could be applied, and because no maintenance record identifies a cause, so any correction would be a rescaling towards a reference rather than the repair of a known fault. The likeliest explanation for a falling response in a quantum sensor left in the field for twenty years is the sensor itself: soiling, or ageing of its diffuser and detector. Analyses that span the last years of this record should allow for several per cent on this account, or use a reference-normalised quantity. Gap-filled records inherit the state of the sensor at the time they were filled and neither add the bias nor remove it.A comparison against
SW_INacross 2013 carries that sensor’s drift, not this one’s. The 47 m pyranometer rises by about 3 % against its own references from 2013, and the ratio between the two tower radiation series moves accordingly. The change is on the pyranometer, see Incoming shortwave radiation at 47 m, but it is visible in any quantity that divides one of these products by the other, such as a photon-to-energy ratio computed over the whole record.The MeteoSwiss series used to fill the gaps changed level in October 2010.
SW_IN_LAE_MSsteps by about 5 % on 6 October 2010, when that station’s radiation instrumentation was rebuilt. This is a property of the reference, not of the tower. It does not degrade the fills, since a driver supplies the state of the sky and a scale change does not alter which half-hours were cloudy. It does mean that a difference between this product and MeteoSwiss Lägern must not be read as evidence about the tower across that date.Nighttime values are exactly zero, not measurements. The sensor reads a small positive offset at night: about 4.2 µmol m-2 s-1 before the 2016 logger replacement and 2.5 µmol m-2 s-1 after it. It is an instrument offset rather than light, and it was removed per day before gap-filling, which sets every measured nighttime record to exactly zero. Analyses of instrument noise or of the offset itself must go back to the screened database series.
2004 is 72 % modelled. The tower record begins 2004-09-20 10:45, and everything before it rests on the
SW_INproduct, which is itself reconstructed for that period. Those records are a fill built on a fill and carry the uncertainty of both steps. The flag marks them.
What the January 2016 changes did
Nothing measurable to this series. Two things happened that month: the tower logger was replaced, which moved TA_T1_47_1 by 1.3 °C, and the fieldbook records a new Kipp & Zonen PAR sensor being installed on 8 January 2016.
That sensor is not this column. The CR1000 logger program measures two incoming-PAR instruments at 47 m and names both. PPFD_IN_T1_47_1, the series exported here, is a Delta-T sunshine sensor, which delivers a signal already scaled to µmol m-2 s-1 and is therefore read at a multiplier of exactly 1. The Kipp & Zonen PAR LITE installed that January is PPFD_IN_T1_47_2, read at the reciprocal of its own calibrated sensitivity, and its record begins on 2016-01-21 14:15 and never reaches back before that date. The maintenance record alone cannot make this distinction, because it files both instruments under the same operation tag.
The Delta-T sensor was installed in August 2004 and appears in every surviving logger program from then on, at the same multiplier of 1 and offset of 0 in both the CR10X and the CR1000 era. The maintenance record shows no replacement and no calibration of it in twenty-one years; two cleanings, in December 2016 and April 2021, are the whole of its documented history.
The data agree. Across 2016 the ratio of this sensor to the tower pyranometer changes by +0.4 % and to MeteoSwiss Lägern by +0.5 %, both smaller than the change the same measurement finds in an ordinary year. The comparison against MeteoSwiss is the one that carries the argument: a change confined to this tower’s acquisition system could move both tower sensors together and leave their ratio flat, but it could not move their ratio against a station 2.5 km away. The one thing that demonstrably did change is the sensor’s nighttime offset, which the per-day correction removes on both sides of the date.
The mst and diive screenings meet at the end of 2021, and that boundary carries no step either. Notebook 03 asserts all of this on every run, so a future change to the product that reintroduced a step would fail rather than export quietly.