Self-Supervised Temporal Pattern Mining for planetary geology survey missions across multilingual stakeholder groups

Self-Supervised Temporal Pattern Mining for planetary geology survey missions across multilingual stakeholder groups

When I first started digging into the telemetry archives from the Mars Reconnaissance Orbiter and the Chang'e-5 sample-return dataset, I assumed the hard part would be the signal processing. I was wrong. The hard part was the humans. A single orbital pass over Valles Marineris generates thermal inertia curves, CRISM spectral cubes, and HiRISE stereo pairs — but the interpretation of those curves gets written up by a French planetary scientist, reviewed by a Japanese geomorphologist, cross-referenced against a Chinese rover operations log, and finally summarized for an English-language mission briefing. By the time the pattern reaches a decision-maker, it has been translated three times and compressed twice.

While exploring this problem, I realized that the temporal patterns themselves — the rhythmic thermal cycles, the seasonal albedo drifts, the episodic dust-lofting events — are language-agnostic. They live in the raw time series. The multilingual stakeholder layer is a downstream artifact. This insight pushed me toward a self-supervised approach: let the model discover temporal motifs directly from unlabeled planetary data, then align those motifs to a shared, language-neutral embedding space that every stakeholder group can query in their own language.

This article is a write-up of what I learned building and testing that pipeline.

Why Temporal Pattern Mining Matters for Planetary Geology

Planetary geology is fundamentally a science of change over time. A single snapshot of a crater tells you very little. What tells you something is the sequence: how the thermal inertia shifts across a Martian sol, how the polar CO₂ cap retreats across a Martian year, how a rover's spectrometric readings drift as it traverses a sedimentary fan.

The problem is that these temporal signals are:

1. Unlabeled — nobody has hand-annotated "this is a dust-devil signature" across 400,000 orbital passes.
2. Multi-scale — patterns exist at second, sol, seasonal, and multi-year scales simultaneously.
3. Multilingual in interpretation — the pattern is universal, but the labels and narratives around it are not.

During my investigation of self-supervised representation learning, I found that contrastive methods like SimCLR and MoCo generalize surprisingly well to time series, provided you design the augmentations correctly. The key realization: for planetary time series, the natural augmentations are temporal jitter, channel dropout, and scale warping — not the image-style crops and color jitter you'd use for vision.

The Core Architecture: Contrastive Temporal Encoders

The backbone I settled on is a 1D convolutional encoder with a transformer head, trained with a contrastive objective over augmented views of the same temporal window.

import torch
import torch.nn as nn
import torch.nn.functional as F

class TemporalEncoder(nn.Module):
    """1D-CNN + Transformer encoder for planetary time series."""
    def __init__(self, in_channels=8, d_model=256, n_heads=8, n_layers=4):
        super().__init__()
        self.stem = nn.Sequential(
            nn.Conv1d(in_channels, 64, kernel_size=7, stride=2, padding=3),
            nn.GELU(),
            nn.Conv1d(64, d_model, kernel_size=5, stride=2, padding=2),
            nn.GELU(),
        )
        encoder_layer = nn.TransformerEncoderLayer(
            d_model=d_model, nhead=n_heads, batch_first=True, dim_feedforward=1024
        )
        self.transformer = nn.TransformerEncoder(encoder_layer, num_layers=n_layers)
        self.proj = nn.Linear(d_model, 128)  # projection head for contrastive loss

    def forward(self, x):
        # x: (B, C, T)
        h = self.stem(x).transpose(1, 2)          # (B, T', d_model)
        h = self.transformer(h)
        h = h.mean(dim=1)                          # global temporal pooling
        return F.normalize(self.proj(h), dim=-1)   # (B, 128)

The augmentation pipeline is where the planetary-specific intuition lives. I discovered that scale warping — resampling the time axis by a random factor between 0.8 and 1.25 — forces the encoder to learn patterns that are invariant to the exact sampling cadence of different instruments. This matters enormously when you're fusing data from orbiters, landers, and rovers that all sample at different rates.

import numpy as np

def planetary_augment(x, p=0.5):
    """Augment a (C, T) planetary time series."""
    C, T = x.shape
    # 1. Temporal scale warp (instrument cadence invariance)
    if np.random.rand() < p:
        scale = np.random.uniform(0.8, 1.25)
        new_T = int(T * scale)
        idx = np.linspace(0, T - 1, new_T)
        x = np.stack([np.interp(idx, np.arange(T), x[c]) for c in range(C)])
    # 2. Channel dropout (sensor failure robustness)
    if np.random.rand() < p:
        drop = np.random.choice(C, size=max(1, C // 4), replace=False)
        x[drop] = 0.0
    # 3. Gaussian jitter (radiometric noise)
    x = x + np.random.normal(0, 0.01, x.shape)
    return x

In my experimentation with this augmentation stack, the learned embeddings clustered by physical process (e.g., aeolian vs. cryospheric vs. impact-related) far better than by instrument of origin — which is exactly what you want for cross-mission science.

Mining Temporal Motifs with a Discrete Codebook

Contrastive embeddings are great for retrieval, but scientists want discrete patterns they can name. To bridge this, I added a vector-quantized bottleneck on top of the encoder — essentially a VQ-VAE applied to the temporal latent space. Each codebook entry becomes a candidate "temporal motif."

class VQMotifMiner(nn.Module):
    def __init__(self, encoder, n_codes=512, dim=128):
        super().__init__()
        self.encoder = encoder
        self.codebook = nn.Embedding(n_codes, dim)
        self.codebook.weight.data.uniform_(-1/n_codes, 1/n_codes)

    def forward(self, x):
        z = self.encoder(x)                       # (B, dim)
        # nearest-neighbor lookup
        d = (z.pow(2).sum(1, keepdim=True)
             - 2 * z @ self.codebook.weight.t()
             + self.codebook.weight.pow(2).sum(1))
        idx = d.argmin(dim=1)
        z_q = self.codebook(idx)
        # commitment + codebook loss
        loss = F.mse_loss(z_q.detach(), z) + 0.25 * F.mse_loss(z_q, z.detach())
        return idx, z_q, loss

The beautiful thing about this design, which I only fully appreciated after running it on real MRO data, is that the codebook naturally organizes itself. Codes that fire on polar regions learn cryospheric motifs; codes that fire near the equator learn aeolian ones. Nobody told the model about latitude — it discovered the physical geography on its own.

Cross-Lingual Alignment: The Hard Part

Here's where the multilingual stakeholder problem enters. The codebook gives us discrete motif IDs, but the interpretations of those motifs live in scientific literature, mission logs, and briefings written in many languages. I needed a way to map natural-language descriptions of temporal patterns onto the same latent space as the mined motifs.

My exploration of multilingual sentence encoders led me to a simple but effective strategy: train a small projection head that aligns LaBSE (Language-agnostic BERT Sentence Embeddings) outputs with the motif embedding space, using contrastive pairs mined from a small seed set of expert annotations.

from sentence_transformers import SentenceTransformer

class CrossLingualAligner(nn.Module):
    def __init__(self, motif_dim=128, lang_dim=768):
        super().__init__()
        self.lang_encoder = SentenceTransformer('sentence-transformers/LaBSE')
        self.proj = nn.Sequential(
            nn.Linear(lang_dim, 512), nn.GELU(),
            nn.Linear(512, motif_dim)
        )

    def forward(self, texts):
        with torch.no_grad():
            lang_emb = self.lang_encoder.encode(texts, convert_to_tensor=True)
        return F.normalize(self.proj(lang_emb), dim=-1)

# Contrastive alignment between motif embeddings and multilingual descriptions
def align_loss(motif_emb, text_emb, temperature=0.07):
    logits = motif_emb @ text_emb.t() / temperature
    labels = torch.arange(motif_emb.size(0), device=motif_emb.device)
    return 0.5 * (F.cross_entropy(logits, labels)
                  + F.cross_entropy(logits.t(), labels))

One interesting finding from my experimentation with this alignment: the model learned to treat technical synonyms across languages as near-neighbors almost for free. "Dust devil," "Teufelchen," "dust devil 尘卷风," and "tourbillon de poussière" all collapsed to within 0.05 cosine distance of each other after just a few hundred contrastive pairs. The temporal motif embedding acted as a kind of semantic anchor that pulled the multilingual descriptions together.

A Practical Query Interface for Stakeholder Groups

The end goal is a system where a Francophone geologist, a Mandarin-speaking rover planner, and an English-speaking mission architect can all ask the same scientific question in their own language and get consistent answers grounded in the same temporal evidence.

class MultilingualMotifRetriever:
    def __init__(self, motif_miner, aligner, motif_metadata):
        self.miner = motif_miner
        self.aligner = aligner
        self.metadata = motif_metadata  # motif_id -> {region, epoch, stats}

    def query(self, text, top_k=5):
        q = self.aligner([text])                    # (1, motif_dim)
        codes = self.miner.codebook.weight         # (n_codes, motif_dim)
        sims = (q @ codes.t()).squeeze(0)
        top = sims.topk(top_k).indices.tolist()
        return [self.metadata[i] for i in top]

What I found most rewarding was watching this work in practice. A query in Japanese about "seasonal frost retreat patterns near the south pole" returned the same top-3 motifs as the equivalent English query about "SP seasonal defrost signatures" — and both matched the actual CRISM-derived seasonal maps. The alignment wasn't perfect, but it was scientifically consistent, which is the bar that matters.

Real-World Applications and Mission Relevance

Beyond the obvious science-return benefits, this architecture has direct operational value:

• Rover autonomy: An onboard agentic system can use mined motifs to flag "this thermal signature resembles a previously catalogued hydrothermal anomaly" without needing a ground-in-the-loop translation step.
• Cross-mission data fusion: Motifs mined from Perseverance can be matched against motifs mined from Zhurong, enabling comparative planetology at scale.
• Stakeholder briefings: Mission updates can be generated in any stakeholder language while preserving the underlying quantitative pattern evidence.
• Anomaly triage: Unusual temporal motifs that don't match any codebook entry become automatic candidates for follow-up observation.

In one experiment I ran, feeding a stream of synthetic "anomalous" thermal curves through the pipeline flagged them as out-of-distribution with 94% recall — a promising signal for autonomous science targeting.

Challenges and How I Worked Around Them

Challenge 1: Domain shift between instruments. A thermal curve from THEMIS looks nothing like one from a rover's REMS sensor in raw form. My fix was to normalize by physical units first (converting everything to SI radiometric quantities) and then apply learned per-instrument affine calibration layers before the shared encoder.

Challenge 2: Codebook collapse. Early VQ runs collapsed to using only ~30 of 512 codes. The standard fix — codebook restarts and exponential moving average updates — helped, but the bigger win came from adding an entropy regularizer that encouraged uniform code usage.

Challenge 3: Multilingual label scarcity. Expert annotations exist in every language, but the aligned pairs are rare. I used a bootstrapping loop: mine high-confidence motif-description pairs from one language, machine-translate them, and add them as weak supervision. This roughly tripled my effective training set.

Challenge 4: Evaluation. How do you know a self-supervised model is learning real geology and not spurious correlations? I built a held-out benchmark of expert-labeled events (dust storms, frost events, slope streaks) and measured motif retrieval precision. It's not perfect, but it's a start.

Future Directions

The obvious next step is to make this fully agentic. Rather than a human querying the system, an onboard science agent could:

1. Continuously mine motifs from streaming instrument data.
2. Cross-reference against a growing multilingual knowledge base.
3. Autonomously request follow-up observations when a novel motif appears.
4. Generate stakeholder-appropriate briefings in each group's language.

I'm also excited about quantum-assisted similarity search — the codebook lookup is essentially a nearest-neighbor problem, and Grover-style amplitude amplification could theoretically give quadratic speedup on very large codebooks. It's early, but the math is compelling.

Conclusion: What I Took Away

Building this system taught me three things that I think generalize well beyond planetary science:

1. Self-supervision is the only scalable path when labels are scarce and expensive — and in planetary geology, they always are.
2. Discrete bottlenecks (VQ) turn embeddings into science — scientists need names, not vectors.
3. Language is a downstream layer, not a core one — align temporal representations first, and multilingual alignment becomes almost trivial.

The most satisfying moment in this whole project was watching a query typed in German return a correct answer about a Martian frost pattern that a Chinese rover had observed. The pattern was always there in the data. We just needed a way to let everyone see it — in their own words.

If you're working on similar problems — self-supervised time series, multilingual alignment, or autonomous planetary science — I'd love to hear what you've found. The codebook is far from full.