Block correlation analysis
When you check the quality of a match between a dendro curve and a reference curve, you should check not only how the two curves match overall, but also how various short blocks (segments) of the two curves match each other. This type of checking is also named "Correlation by segment".
Blocks (segments) of the curve being tested are defined with a selectable length (e.g. 30) and with differing starting points, e.g. lagged by 10 years. I.e. starting at 0 (0-9), 10 (10-39), 20 (20-49), 30 (30-59) etc. This means that the blocks being tested may overlap.
In a CDendro "Block correlation analys" we also find out where these blocks match best and next best and next-next best towards the reference. The results are useful when the curve being tested is not already crossdated. Then the block check may reveal a missed or extra ring, see example below.
Here is the result of an attempt to crossdate a curve towards a reference. At first there is no reasonable match at all!
SN009A_of_D:\ake\tree\sn\SNMEAS.rwl using No detrend
compared to the reference
Namdo_1 using No detrend Dated to 1995
Minimum overlap used when finding best match: 50
Table sorted by Proportion of last two years growth (2,0,T) (P2Yrs)/TTest
--Rel Over *P2Yrs------ (year)
-year lap CorrC TTest
191 123 0.31 3.6 (1804)
313 99 0.32 3.4 (1682)
255 123 0.27 3.1 (1740)
331 81 0.32 3.0 (1664)
-18 105 0.27 2.8 (2013)
51 123 0.24 2.7 (1944)
63 123 0.23 2.7 (1932)
251 123 0.23 2.6 (1744)
340 72 0.29 2.5 (1655)
SN009A_of_D:\ake\tree\sn\SNMEAS.rwl compared to the reference Namdo_1
Best matches for the whole sample: 191 3.63 (1804) 313 3.35 (1682) 255 3.08 (1740)
This sample is not dated so the best match is used as "Aimed at"
Block length: 30 Table sorted by Proportion of last two years growth (2,0,T) (P2Yrs)/TTest
Block -----Aimed -------Best ------------Three best matches with {hitAt,Prop2Yrs,SetsSampleTo}---------
start --------at around that ---1stBestMatch------- ---2ndBestMatch------- ---3rdBestMatch-------
0 191 0.27 191 0.27 139 0.49 139 (1856) 61 0.46 61 (1934) 32 0.46 32 (1963)
10 201 0.33 201 0.33 16 0.62 6 (1989) 287 0.44 277 (1718) 6 0.43 -4 (1999)
20 211 0.39 211 0.39 26 0.72 6 (1989) 271 0.60 251 (1744) 93 0.51 73 (1922)
30 221 0.23 220 0.29* 36 0.70 6 (1989) 281 0.59 251 (1744) 370 0.54 340 (1655)
40 231 0.32 231 0.32 46 0.54 6 (1989) 371 0.52 331 (1664) 260 0.47 220 (1775)
50 241-0.05 242 0.18* 381 0.55 331 (1664) 73 0.49 23 (1972) 186 0.48 136 (1859)
60 251-0.06 252 0.20* 315 0.60 255 (1740) 83 0.48 23 (1972) 233 0.41 173 (1822)
70 261-0.04 260 0.04* 75 0.70 5 (1990) 289 0.57 219 (1776) 325 0.49 255 (1740)
80 271 0.44 271 0.44 85 0.72 5 (1990) 337 0.57 257 (1738) 162 0.56 82 (1913)
90 281 0.63 281 0.63 95 0.78 5 (1990) 281 0.63 191 (1804) 145 0.61 55 (1940)
All SetsSampleTo alternatives sorted:
1655 1664 1664 1718 1738 1740 1740 1744 1744 1775 1776 1804 1822 1856 1859 1913 1922
1934 1940 1963 1972 1972 1989 1989 1989 1989 1990 1990 1990 1999
Do notice the year-group 1989-1990 alternative, which corresponds to a reasonable match for eight of our ten 30 years long blocks! The jump from 1989 to 1990 is because of a false ring that should be removed. After we have removed that ring from our measurements we get these results:
Minimum overlap used when finding best match: 50
Table sorted by Proportion of last two years growth (2,0,T) (P2Yrs)/TTest
--Rel Over *P2Yrs------ (year)
-year lap CorrC TTest
6 123 0.60 8.3 (1989)
32 123 0.37 4.4 (1963)
258 123 0.28 3.2 (1737)
142 123 0.26 2.9 (1853)
331 82 0.31 2.9 (1664)
-46 77 0.29 2.6 (2041)
289 123 0.23 2.6 (1706)
340 73 0.29 2.6 (1655)
127 123 0.22 2.5 (1868)
There is a match at relative year 6 i.e. at 1989
SN009A_of_D:\ake\tree\sn\SNMEAS.rwl compared to the reference Namdo_2
Best matches for the whole sample: 6 8.32 (1989) 32 4.41 (1963) 258 3.16 (1737)
This sample is not dated so the best match is used as "Aimed at"
Block length: 30 Table sorted by Proportion of last two years growth (2,0,T) (P2Yrs)/TTest
Block -----Aimed -------Best ------------Three best matches with {hitAt,Prop2Yrs,SetsSampleTo}---------
start --------at around that ---1stBestMatch------- ---2ndBestMatch------- ---3rdBestMatch-------
0 6 0.41 6 0.41 139 0.49 139 (1856) 61 0.46 61 (1934) 32 0.46 32 (1963)
10 16 0.62 16 0.62 16 0.62 6 (1989) 287 0.44 277 (1718) 6 0.43 -4 (1999)
20 26 0.72 26 0.72 26 0.72 6 (1989) 271 0.60 251 (1744) 93 0.51 73 (1922)
30 36 0.70 36 0.70 36 0.70 6 (1989) 281 0.59 251 (1744) 370 0.54 340 (1655)
40 46 0.54 46 0.54 46 0.54 6 (1989) 371 0.52 331 (1664) 260 0.47 220 (1775)
50 56 0.40 56 0.40 330 0.55 280 (1715) 114 0.54 64 (1931) 5 0.52 -45 (2040)
60 66 0.34 66 0.34 124 0.59 64 (1931) 122 0.46 62 (1933) 202 0.46 142 (1853)
70 76 0.70 76 0.70 76 0.70 6 (1989) 328 0.53 258 (1737) 359 0.52 289 (1706)
80 86 0.69 86 0.69 86 0.69 6 (1989) 126 0.60 46 (1949) 76 0.58 -4 (1999)
90 96 0.79 96 0.79 96 0.79 6 (1989) 282 0.71 192 (1803) 146 0.53 56 (1939)
All SetsSampleTo alternatives sorted:
1655 1664 1706 1715 1718 1737 1744 1744 1775 1803 1853 1856 1922 1931 1931 1933 1934
1939 1949 1963 1989 1989 1989 1989 1989 1989 1989 1999 1999 2040
Block checking may also be useful when doing a quality analysis of e.g. an old published reference curve. When all blocks match properly towards another reference curve, then that old published curve may be correct. Though if the late end tail of the curve matches towards one time in the other reference, and the early end tail matches towards quite another time, then we may suspect that samples from different times were mixed together when that old published reference curve was originally created.