Using Active Learning to Quantify how Training Data Errors Impact Classification Accuracy over Smallholder-Dominated Agricultural Systems

Using active learning to quantify how training
data errors impact classification accuracy over
smallholder-dominated agricultural systems
Stephanie Debats, Lei Song, Su Ye, Sitian Xiong, Kaixi Zhang,
Tammy Woodard, Ron Eastman, Ryan Avery, Kelly Caylor,
Dennis McRitchie, Lyndon Estes
Clark University|Clark Labs
University of California Santa Barbara

AWS Cloud Credits for Research Program
IIASA

Stephanie Debats Ryan Avery Su YeLei Song Sitian Xiong

Problem 1: High spatial variability

Problem 2: High temporal variability
Bing Base Map
PlanetScope Analytic

Problem 3: Interpretation errors in training data

High spatial & temporal resolution imagery

Active Learning
01
00
11
Train
Predict
Select
Re-label
Label
Debats et al, 2017

Labelling component:
Crowdsourcing Platform

True positive (TP) False positive (FP) False negative (FN) True negative (TN)

score = in_accuracy * β0 +
out_accuracy * β1 +
fragmentation * β2 +
edge_accuracy * β3 +
categorical_accuracy * β4

Accuracy assessment and consensus labelling
Probability

Bayesian Model Averaging
Label collection
! " # = % ! &' # !("|#, &')
,
'-.

Bayesian Model Averaging
Heat map
! " # = % ! &' # !("|#, &')
,
'-.

Debats et al (2016)
A generalized computer vision approach to mapping crop fields in
heterogeneous agricultural landscapes
Remote Sensing Environment 179
Machine Learning component
1. On the fly feature extraction
2. Spark ML RandomForest
GeoTrellis/
GeoPySpark

Does Training Data Error Impact Classification Performance?

Next Steps
1. Errors in image atmospheric corrections
2. Increase feature space for classifier
3. Improve label quality
4. Quantify gap between worker and ground

Worker map
Ground truth(y)
Where lies the truth?

8
Circle Bias, many
false positive
identified because
of overreliance on
circular features
https://github.com/ecoh
ydro/CropMask_RCNN

Probability
score above
.7 deemed a
center pivot
Tested on
never before
seen
512x512 tiles
11
Some center
pivots are
missed
because of
date mismatch
between
imagery and
labels of the
reference
dataset

BAYESIAN MODEL AVERAGING:
! " # = %
&'(
)
! *& # !("|#, *&)
": the ground truth, which will be either ‘field’ or ‘no field’
#: the given data of crowdsourcing opinions for labeling this pixel
(e.g., # = {#mapper_1 = field , #mapper_/= no field, …} )
*&: the Mappers considered
(1) 012234&’s opinion: how much probability to
be "
(2) Weight (or evidence): is the probability that we weigh
012234&’s opinion based on their mapping history
combining crowdsourcing labels from their mapping history

MAPPER OPINION
In our mapping project, mappers are allowed to only label a crispy category for polygons (either ‘field’ or ‘no
field’). So ! " #, %& = 0 )* 1
(1) !(" = -./01|#& = -./01, %&) = 1
(2) !(" = 4) -./01|#& = -./01, %&) = 0
(3) !(" = 4) -./01|#& = 4) -./01, %&) = 1
(4) !(" = -./01|#& = 4) -./01, %&) = 0

WEIGHT
Weight: ! "# $ ∝ ! $ "# !("#)
(1) !("#): ‘mapper priors’, is our prior belief for mapper '. We can use average score
(combining geometric and thematic accuracy) to represent our belief
(()*) ∝ (∑,-.
/
01234,) /7
(2) ! $ "# : ‘mapper likelihood’, ! $ "# ∝ exp(-
.
8
9:;#) [1][2]
BIC(Bayesian Information Criterion) = ln ? ∗ A − 2 ln D $ ̂F, "
‘BIC simply reduces to maximum likelihood when the number of parameters is equal
for the models of interest’ [3] , so 9:; ≈ −2 ln D $ IF, " . After adjustment,
( J )* ∝ K J ̂F, )* (Maximum mapper likelihood)
(? is the sample number, A
is the parameter number to
be estimated (our case has
only one, i.e., L), ML is the
label that maximizes the
likelihood function)

WEIGHT (CONTI.)
Weight: ! "# $ ∝ ! $ "# !("#)
Mapper likelihood: ' ( )* ∝ + ( ,-, )* (Maximum Mapper likelihood)
(1) !(- = 01234| ,-, "#) = ! $ = 01234 - = 01234, "# = (∑8
9 :;<
:;<=>?<
) /A
(2) !(- = BC 01234| ,-, "#) = ! $ = BC 01234 - = BC 01234, "# = (∑8
9 :?<
:?<=>;<
) /A
D $ ̂-, " can be computed as:
* Maximum mapper likelihood is actually average producer’s accuracy of the mapper

SUMMARY
! " # = ∑&'(
)
! *& # !("|#, *&)
weight = score ∗ producer′s accuracy ∝ P M8 D
P("|D, M8) = 0 ;< 1
Labeling:
If ! " = >?@AB # > ! " = D; >?@AB # (or ! " = >?@AB # > 0.5), we give a consensus label
as field; otherwise, we give a label as no field
The posterior probability of the pixel label " given the data of mappers’ opinions (#):
(*& is the mapper ?)
→ ! " # =
∑FGH
I
JK&LMNF∗ O(P|Q,RF)
∑FGH
I
JK&LMNF
, where

Using Active Learning to Quantify how Training Data Errors Impact Classification Accuracy over Smallholder-Dominated Agricultural Systems

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Using Active Learning to Quantify how Training Data Errors Impact Classification Accuracy over Smallholder-Dominated Agricultural Systems